AUGUST,  1916  BULLETIN  379 

CORNELL  UNIVERSITY 
AGRICULTURAL    EXPERIMENT   STATION 


BLACK  ROT,  LEAF  SPOT,  AND  CANKER  OF 
POMACEOUS  FRUITS 


L.  R.  HESLER 


H45 


ITHACA,  NEW  YORK 
PUBLISHED  BY  THE  UNIVERSITY 


(Ulip  i.  m.  Itil  ffitbrarg 


Nortij  (Earnlina  ^UU  IniaprHtty 

337:5;: 
H45 


AUGUST,  1916 


BULLETIN  379 


CORNELL  UNIVERSITY 
AGRICULTURAL   EXPERIMENT   STATION 


BLACK  ROT,  LEAF  SPOT,  AND  CANKER  OF 
POMACEOUS  FRUITS 


L.  R.  HESLI 


OCT  6       f( 

THIS  BOOK  IS  DUE  ON  THE  DAT 
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ITHACA,  NEW 
PUBLISHED  BY  THE 


D.  H.  HILL 


CORNELL  UNIVERSITY 

AGRICULTURAL  EXPERIMENT  STATION 

Experimenting  Staff 

ALBERT  R.  MANN,  B.S.A.,  A.M.,  Acting  Director. 
"HENRY  H.  WING,  M.S.  in  Agr.,  Animal  Husbandry. 
T.  LYTTLETON  LYON,  Ph.D.,  Soil  Technology. 
JOHN  L.  STONE,  B.Agr.,  Farm  Practice. 
JAMES  E.  RICE,  B.S.A.,  Poultry  Husbandry. 
GEORGE  W.  CAVANAUGH,  B.S.,  Agricultural  Chemistry. 
HERBERT  H.  WHETZEL,  M.A.,  Plant  Pathology. 
ELMER  O.  PIPPIN,  B.S.A.,  Soil  Technology. 
G.  F.  WARREN,  Ph.D.,  Farm  Management. 
WILLIAM  A.  STOCKING,  Jr.,  M.S.A.,  Dairy  Industry. 
WILFORD  M.  WILSON,  M.D.,  Meteorology. 
RALPH  S.  HOSMER,  B.A.S.,  M.F.,  Forestry. 
JAMES  G.  NEEDHAM,  Ph.D.,  Entomology  and  Limnology. 
ROLLINS  A.  EMERSON,  D.Sc,  Plant  Breeding. 
HARRY  H.  LOVE,  Ph.D.,  Plant  Breeding. 
ARTHUR  W.  GILBERT,  Ph.D.,  Plant  Breeding. 
DONALD  REDDICK,  Ph.D.,  Plant  Pathology. 
EDWARD  G.  MONTGOMERY,  M.A.,  Farm  Crops. 
WILLIAM  A.  RILEY,  Ph.D.,  Entomology. 
MERRITT  W.  HARPER,  M.S.,  Animal  Husbandry. 
JAMES  A.  BIZZELL,  Ph.D.,  Soil  Technology. 
GLENN  W.  HERRICK,  B.S.A.,  Economic  Entomology. 
HOWARD  W.  RILEY,  M.E.,  Farm  Mechanics. 
CYRUS  R.  CROSBY,  A.B.,  Entomology. 
HAROLD  E.  ROSS,  M.S.A.,  Dairy  Industry. 
KARL  McK.  WIEGAND,  Ph.D.,  Botany. 
EDWARD  A.  WHITE,  B.S.,  Floriculture. 
WILLIAM  H.  CHANDLER,  Ph.D.,  Pomology. 
ELMER  S.  SAVAGE,  M.S.A.,  Ph.D.,  Animal  Husbandry. 
LEWIS  KNUDSON,  Ph.D.,  Plant  Physiology. 
KENNETH  C.  LIVERMORE,  Ph.D.,  Farm  Management. 
ALVIN  C.  BEAL,  Ph.D.,  Floriculture. 
MORTIER  F.  BARRUS,  Ph.D.,  Plant  Patholofry. 
CLYDE  H.  MYERS,  M.S.,  Ph.D.,  Plant  Breeding. 
GEORGE  W.  TAILBY,  Jr.,  B.S.A.,  Superintendent  of  Livestock. 
EDWARD  S.  GUTHRIE,  M.S.  in  Agr.,  Ph.D.,  Dairy  Industry. 
JAMES  C.  BRADLEY,  Ph.D.,  Entomology. 
PAUL  WORK,  B.S.,  A.B.,  Vegetable  Gardening. 
JOHN  BENTLEY,  Jr.,  B.S.,  M.F.,  Forestry. 
EARL  W.  BENJAMIN,  Ph.D.,  Poultry  Husbandry. 
EMMONS  W.  LELAND,  B.S.A.,  Soil  Technology. 
CHARLES  T.  GREGORY,  Ph.D.,  Plant  Pathology. 
WALTER  W.  FISK,  M.S.  in  Agr.,   Dairy  Industry. 
ARTHUR  L.  THOMPSON,  Ph.D.,  Farm  Management. 
LEX  R.  HESLER,  A.B.,  Ph.D.,  Plant  Pathology. 
ROBERT  MATHESON,  Ph.D.,  Entomology. 
MORTIMER  D.  LEONARD,  B.S.,  Entomology. 
FRANK  E.  RICE,  Ph.D.,  Agricultural  Chemistry. 
VERN  B.  STEWART,  Ph.D.,  Plant  Pathology. 

IVAN  C.JAGGER,  M.S.  in  Agr.,  Plant  Pathology  (In  cooperation  with  Rochester  University). 
CHARLES  H.  HADLEY,  Jr.,  B.S.,  Entomology. 
DANIEL  S.  FOX,   B.S.,  Farm  Management. 
WILLIAM  I.   MYERS,  B.S.,   Farm  Management. 
LEW  E.  HARVEY,  B.S.,  Farm  Management. 
LEONARD  A.  MAYNARD,  A.B.,  Ph.D.,  Animal  Husbandry. 
LOUIS  M.   MASSEY,  A.B.,  Plant  Pathology. 
BRISTOW  ADAMS,  B.A.,  Editor. 
LELA  G.  GROSS,  Assistant  Editor. 
The  regular  bulletins  of  the  Station  are  sent  free  on  request  to  residents  of  New  York  State. 

50 


CONTENTS 

PAGE 

Host  considerations 53 

Plants  concerned 53 

Varietal  susceptibility 53 

Of  fruit  to  black  rot 53 

Of  foliage  to  leaf  spot 53 

Of  limbs  to  canker 53 

The  disease 54 

Names 54 

History 54 

The  black  rot  of  the  fruit 54 

The  leaf  spot 55 

The  canker  form 55 

Geographical  occurrence 56 

Economic  importance 58 

General  considerations ' 58 

Nature  of  losses 58 

Injury  to  fruit 58 

Injury  to  foliage 59 

Injury  to  limbs 59 

Symptoms 60 

On  the  fruit 60 

On  the  leaves. .  .^ 61 

On  the  limbs 62 

Other  organs  affected 63 

Etiology 64 

Morphology' , 64 

Perithecia 64 

Pycnidia 66 

Pycnidial  format!cn 68 

Pycnospores 71 

Mycelium 74 

Sclerotia 75 

Chlamydosporc:: 75 

Microconidia 76 

Yeast  forms 76 

Physiology 77 

Methods  of  isolation 77 

Cultural  characters  — ■  general 77 

Cultural  characters  —  speciril 77 

Protoplasmic  streaming 77 

Pathogenicity 78 

Black  rot  of  apple 78 

Leaf  spot  of  apple 79 

Canker  of  apple 87 

Cross-inoculations  and  host  relationships 95 

Names  and  synonymy 99 

Life  history  studies loi 

Source  of  the  inoculum loi 

Method  of  spore  discharge 1 03 

Time  of  spore  discharge 104 

Agents  of  dissemination 105 

Infection  courts 105 

Pycnospore  germination 1 07 

Ascospore  germination 108 

Incubation  period 108 

51 


52  Contents 

PAGE 

Pathological  histology 1 09 

Fruit 109 

Leaves no 

Bark 1 1 1 

Control ' 116 

Black  rot 116 

Exclusion  by  legislation 116 

Spraying 116 

HandHng  of  fruits 117 

Storage 1 17 

Leaf  spot 117 

Spraying 1 1 7 

Cultivation 118 

Canker 118 

Historical  and  introductory ' 118 

Surgical  methods 119 

Pruning 119 

Removal  of  limbs 119 

Removal  of  diseased  bark 120 

Wound  treatment 120 

Wound  disinfection 120 

Wound  protection 120 

Wound  heahng 123 

Wound  cork 123 

Wound  wood 123 

Callus 123 

Spraying 124 

General  considerations 124 

Orchard  management 125 

Resistant  varieties 125 

An  enemy  of  the  pathogenc 126 

Bibliography 126 


BLACK  ROT,  LEAF  SPOT,  AND  CANKER  OF  POMACEOUS 
FRUITS' 

L.  R.  Hesler 

HOST  CONSIDERATIONS 
PLANTS  CONCERNED 

The  black  rot,  leaf  spot,  and  canker  of  pomaceous  fruits  is  primarily 
a  disease  of  the  apple,  Pyrus  Malus  L.  It  affects  other  trees  also,  however, 
especially  the  pear  {Pyrus  communis  L.),  the  quince  {Cydonia  vulgaris 
Pers.),  and  the  crab  {Pyrus  coronaria  L.),  showing  on  these  hosts  symp- 
toms similar  to  those  on  the  apple.  In  addition  the  pathogene  infests 
the  dead  parts  of  a  great  variety  of  other  trees  and  shrubs,  but  in  such 
cases  there  is  usually  no  evidence  that  it  has  been  the  causal  factor  in  the 
death  of  the  tissues.  In  the  State  of  New  York,  at  least,  this  disease 
is  of  economic  importance  only  on  aj^ple  trees. 

VARIETAL  SUSCEPTIBILITY 
OF  FRUIT  TO  BLACK  ROT 

The  summer  varieties  of  apples  are  affected  by  black  rot  at  the  time  of 
ripening,  while  winter  varieties  commonly  suffer  in  storage.  In  Con- 
necticut black  rot  is  a  most  troublesome  storage  rot  (Clinton,  1915:  5). ^ 

OF  FOLIAGE  TO  LEAF  SPOT 

Brooks  and  DeMeritt  (1912:183),  in  New  Hampshire,  note  striking 
differences  in  the  varietal  resistance  of  apple  seedlings  to  leaf  spot.  In 
Virginia,  Ben  Davis  and  Black  Twig  are  more  severely  attacked  than  are 
other  varieties  (Reed,  Cooley,  and  Rogers,  1912:5).  Salmon  (1907), 
writing  from  England,  states  that  among  the  varieties  most  affected 
there  are  Peasgood,  Nonsuch,  Cox's  Orange,  and  others.  The  writer  has 
noted  that  Chenango,  Baldwin,  Rhode  Island,  and  Twenty  Ounce  show 
spotted  foliage  more  commonly  in  New  York  than  do  other  varieties. 

OF  LIMBS  TO  CANKER 

Varieties  of  apples  exhibit  a  marked  difference  in  susceptibility  to  the 
disease,  and  this  variation  is  not  the  same  with  respect  to  the  different 
parts  affected.  In  western  New  York  Twenty  Ounce  is  the  variety  most 
severely  affected  by  the  canker.  This  variety  is  rarely  found  unaffected 
by  canker,  even  in  orchards  that  are  managed  according  to  improved 
methods.     Neglected  trees  of  the  Twenty  Ounce  variety  are  often  killed. 

1  Also  presented  to  the  Faculty  of  the  Graduate  School  of  Cornell  University,  May,  1914,  as  a  major 
thesis  in  partial  fulfillment  of  the  requirements  for  the  degree  of  doctor  of  philosophy. 

2  Dates  in  parenthesis  refer  to  bibliography,  page  126. 

53 


54  Bulletin  379 

Paddock  (1899  b:  181)  says  that  certain  growers  in  New  York  State  have 
noted  that  Twenty  Ounce  is  most  Hkely  to  be  attacked.  He  Hsts  other 
varieties  in  order  of  their  susceptibiHty,  as  follows:  Baldwin,  Wagener, 
Rhode  Island,  Tompkins  King.  Regarding  the  Esopus,  Paddock 
(1899b:  180)  says  that  this  variety  has  apparently  run  out  because  of  this 
disease.  In  Ontario,  Ben  Davis,  Northern  Spy,  and  other  varieties  are 
severely  injured  by  the  disease  (McCready,  1910). 

THE  DISEASE 

NAMES 

The  disease  on  the  fruit  is  called  black  rot,  ring  rot,  blossom-end  rot, 
and  brown  rot.  The  first  name  is  descriptive  and  definite,  and  seems 
desirable. 

Lesions  on  the  foliage  are  termed  leaf  spot,  brown  spot,  and  frog-eye. 

The  names  apple  canker,  black  rot  canker,  and  New  York  apple  tree 
canker,  are  most  commonly  applied  to  the  disease  when  it  occurs  on  the 
bark.  The  term  apple  canker  needs  some  qualification,  since  many  kinds 
of  cankers  occur  on  the  apple.  It  was  under  such  an  exigency  that 
Paddock  (1899b:  180,  footnote)  first  used  the  name  New  York  apple  tree 
canker.  The  writer  prefers  to  use  this  name  regardless  of  its  length,  not 
alone  because  of  priority,  but  also  because  of  general  usage. 

HISTORY 
THE  BLACK  ROT  OF  THE  FRUIT 

The  disease  on  the  fruit  was  observed  by  Peck  (1879:20)  in  Schoharie 
County,  New  York,  and  he  quotes  the  remark  of  stagecoach  passengers 
that  they  "never  before  knew  of  apples  rotting  on  the  tree."  Arthur 
(1885)  records  black  rot  of  quince  fruit  at  Geneva,  New  York,  and  notes 
the  importance  and  infectious  nature  of  the  disease.  Scribner  (1890) 
notes  the  disease  in  New  Jersey  and  describes  the  symptoms  and  causal 
nature.  The  same  year  Baccarini  (1890),  in  Italy,  observed  the  rotting 
of  otherwise  sound  apples,  pears,  and  peaches,  the  decay  occurring  in  a 
storeroom  of  fruit  gathered  when  ripe;  this  was  a  new  appearance  of  the 
disease  in  that  country.  Two  years  later  Halsted  (1892)  discussed  the 
black  rot  of  quince  in  New  Jersey.  Sturgis  (1893,  a  and  b)  notes  the 
disease  on  quinces  in  Connecticut  in  August,  1892,  and  later  (1894) 
confirms  the  work  of  Halsted.  Kinney  (1895  c)  figures  and  describes  the 
disease  in  Rhode  Island.  In  the  same  year  it  became  an  object  of  control 
measures  in  Kentucky  (Garman,  1895).  Black  rot  of  apple  is  reported  by 
Burrill  and  Blair  (1901)  in  Illinois;  they  give  a  careful  description  of  the 
disease  and  distinguish  it  from  other  apple  rots.  The  following  year 
Clinton  (1902),  writing  from  the  same  station,  remarks  that  the  disease  on 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits      55 

apples  had  attracted  attention  for  several  years,  and  that  it  was  known 
to  have  occurred  in  Illinois  at  least  as  early  as  1879.  The  disease  as  a 
storage  rot  was  studied  by  Lamson  (1902)  in  New  Hampshire  the  same 
year.     Faurot  (19 12)  describes  the  disease  in  Missouri. 

W.  A.Orton  (1904,  1905, 1906,  1907)  publishes  records  of  the  black  rot  of 
pome  fruits,  the  reports  having  come  to  him  chiefly  from  the  Middle  West. 
In  1905  the  black  rot  of  quince  and  pear  was  especially  injurious  in  Ohio. 
Evans  (19 10)  called  the  attention  of  the  apple  growers  of  South  Africa 
to  the  disease,  which  had  just  been  found  on  apples  at  Grahamstown  and 
also  in  a  consignment  of  apples  from  Sidney,  Australia.  He  urged  the 
importance  of  excluding  the  disease  from  the  Transvaal.  Recent  studies 
on  black  rot  have  been  reported  by  Wolf  (19 13)  in  Alabama. 

the  leap  spot 

The  earliest  record  which  the  writer  has  found  concerning  the  leaf  spot 
is  that  by  Alwood  (1892),  who  reports  brown  spot  of  apple  foliage  in 
Virginia.  He  had  noticed  it  for  several  years  but  states  that  it  was  not 
serious  until  1891,  when  an  outbreak  occurred  over  the  State.  Kinney 
(1895  b)  describes  the  disease  in  Rhode  Island  on  apple  and  pear  leaves,  and 
says  that  it  was  very  common  in  that  State  in  1895.  Stewart  (1896) 
reports  having  found  the  disease  on  Long  Island  in  May,  1895;  he  notes 
that  it  had  been  observed  in  1894  at  Westbury,  Long  Island,  by  Professor 
Beach.  Lamson  (1899)  lists  the  disease  from  New  Hampshire  and 
reports  it  as  having  done  serious  damage  in  some  cases.  Corbett  (1900) 
reports  "  brown  spot,"  or  "  frog-eye,"  as  common  throughout  the  southern 
and  eastern  counties  of  West  Virginia,  and  as  being  more  injurious  than 
either  bHght  or  scab.  Stewart  and  Eustace  (1902)  studied  the  cause  and 
control  of  leaf  spot  in  the  eastern  United  States.  The  same  year  Clinton 
(1902)  notes  the  severity  of  the  disease  in  Illinois,  and  later  (Clinton, 
1904)  he  reports  its  common  occurrence  in  Connecticut.  Stone  and 
Smith  (1903)  record  it  as  one  of  the  most  noticeable  diseases  of  the  season 
of  1902  in  Massachusetts.  Scott  and  Quaintance  (1907)  report  the 
spotting  of  apple  foliage  in  the  Ozark  region,  and  in  the  following  year 
there  appeared  a  more  extensive  work  on  the  leaf  spot  problem  by  Scott 
and  Rorer  (1908).  Work  on  the  leaf  spot  was  begun  in  New  Hampshire 
in  1908  by  I.  M.  Lewis  (1908);  this  investigation  was  carried  further  by 
Brooks  and  DeMeritt  (19 12),  who  report  it  in  full.  Recent  work  on  the 
leaf  spot  form  of  this  disease  has  been  published  in  Virginia  by  Crabill 
(1915)- 

the  canker  form 

According  to  Paddock  (i899.b:  180),  orchardists  have  been  familiar 
with  this  canker  disease  for  years.     Attention  was  first  called  to  the 


56  Bulletin  379 

injury  by  Waite  (1898  a),  in  a  paper  read  at  the  meeting  of  the  Western 
New  York  Horticultural  Society  in  1898.  In  the  spring  of  1898,  Paddock 
(1898,  a  and  b,  and  1899  a)  began  investigations  which  extended  through 
two  seasons.  He  records  having  noticed  the  disease  as  early  as  1891, 
and  says  that  it  became  important  about  1895.  In  1897,  according  to 
Paddock  (1899  b:  192),  considerable  "twig  blight"  was  found  at  Odessa, 
New  York. 

Mangin  (1901)  reports  the  disease  in  France  on  branches  of  apples, 
describing  its  symptoms  in  order,  as  he  says,  to  put  horticulturists  on 
guard  against  invasion  of  the  country  by  the  pathogene.  The  same  year 
Chester  (1901,  a  and  b),  in  Delaware,  observed  what  he  believed  to  be 
the  same  disease  on  apples  and  pears.  His  attention  had  been  called  to 
the  canker  on  the  latter  host  in  the  spring  of  1900,  near  Smyrna.  His 
illustrations  suggest  the  possibility  that  the  disease  was  the  super- 
ficial bark  canker  of  Edgerton  (1908).  A  few  years  later  Lochhead 
(1905)  described  the  disease  in  Canada.  Clinton  (1907),  writing  from 
Connecticut,  states  that  his  attention  was  called  to  a  peculiar  disease 
of  apple  limbs  in  the  spring  of  1906. 

Another  record  of  the  disease  which  has  appeared  from  France  is  that 
by  Griffon  and  Maublanc  (1910).  They  note  very  serious  injury  to 
pears  in  that  country,  and  assert  that  at  the  national  school  of  agriculture 
the  disease  was  first  known  in  1908.  A  study  of  the  disease  was  taken 
up  in  Canada  by  Bethune  (1909).  He  reports  a  great  amount  of  damage 
from  cankers  in  the  region  east  of  Toronto.  The  following  year  a 
synopsis  of  the  investigations  in  the  province  of  Ontario  was  published 
by  McCready  (1910).  A  point  of  interest  noted  in  this  paper  is  that  the 
great  freeze  of  1 903-1 904  in  Prince  Edward  County  marked  the  beginning 
of  the  canker  epiphytotic  there.  The  disease  has  received  further  attention 
in  France  by  Arnaud  (19 12),  who  lists  it  as  occurring  on  a  number  of 
different  plants. 

GEOGRAPHICAL  OCCURRENCE 

The  disease  has  a  very  general  distribution  throughout  the  temperate 
regions  of  the  globe.  Heretofore  it  has  been  regarded  as  a  disease  peculiar 
to  eastern  and  middle  western  America,  but  it  is  now  apparent  that  its 
limit  is  no  longer  to  be  so  regarded.  It  has  been  found  in  Canada,  par- 
ticularly in  Ontario  (Bethune,  1909),  Quebec  (Lochhead,  1905  and  1909), 
and  Nova  Scotia  (Plant  Pathology  Herb.,  Cornell  University  Exsicc- 
no.  2657,  and  Giissow,  letter  to  the  writer).  It  occurs  in  Europe  from 
Italy  to  England,  according  to  the  observations  of  Shear  (1913:81-82). 
From  England  Berkeley  (1836)  reports  it  on  apple  fruit,  while  Salmon 
(1907)  found  it  on  apple  foliage.  It  is  unknown  in  Norway  (Schoyen, 
letter  to  the  writer),  while  both  Ravn  and  Lind  (letters)  state  that  it 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits      57 

is  not  present  in  Denmark.  From  Russia  the  disease  has  been  reported 
by  Potebnia  (1907  and  19 10).  Jaczewsky  (letter  to  the  writer)  states 
that  the  black  rot  and  canker  forais  occur  in  the  provinces  of  Kharkof 
and  Tchernigof,  and  in  the  Transcaucasian  and  Turkestan  regions. 
Potebnia  (letter)  has  collected  all  the  forms  in  Kursk,  near  the  city  of 
Fatej,  and  states  it  as  his  opinion  that  the  disease  occurs  generally  through- 
out Russia.  Bubak  (1909)  reports  it  from  Austria-Hungary.  It  probably 
occurs  in  Switzerland,  Germany,  and  Holland,  according  to  the  general 
statement  of  Shear  ( 19 13 :  82).  Kirchner  (1906 :  440)  hsts  it  from  Germany. 
It  may  not  be  prevalent  there,  however,  for  Hollrung  (letter)  says  the 
disease  is  not  well  known  in  Sachsen.  Its  occun-ence  in  France  is  reported 
by  Arnaud  (1912)  and  others.  The  black  rot  form  has  been  collected  in  the 
vicinity  of  Brussels,  Belgium,  by  Bommer  and  Rousseau  (1885).  Some 
years  ago  it  was  introduced  into  Cape  Colony  from  New  South  Wales 
(Evans,  1910:62,  footnote). 

So  far  as  the  writer  has  been  able  to  ascertain,  the  disease  is  widely 
distributed  in  America.  It  does  not  occur,  however,  so  far  as  indicated 
by  results  from  a  circular  letter  sent  to  the  plant  pathologists  of  the  state 
agricultural  experiment  stations,  in  the  following  States:  Arizona,  Colorado. 
Florida,  Idaho,  Louisiana,  Montana,  Nevada,  North  Dakota,  South 
Dakota,  Tennessee,  Utah,  Washington,  Wyoming,  and  possibly  Oregon. 
The  canker  form  is  commonest  in  the  East,  especially  in  New  York, 
while  fruit  rot  seems  to  occur  more  frequently  in  the  New  England  and 
Middle  Atlantic  sections,  although  Wilson  (19 13)  reports  its  occurrence 
throughout  North  America  east  of  the  Rocky  Mountains.  In  the  Middle 
Western  States,  particularly  Ohio  and  Indiana,  the  pear  and  quince, 
as  well  as  the  apple,  appear  to  have  suffered  considerably.  Quaintance 
and  Scott  (19 12)  state  that  the, leaf  spot  occurs  in  all  sections  east  of  the 
Rocky  Moimtains  where  the  apple  is  grown.  In  another  publication 
Scott  (19 1 2)  asserts  that  it  is  found  in  all  humid  sections  of  America. 
According  to  Reed,  Cooley,  and  Rogers  (1912:3-4),  "frog-eye"  is  wide- 
spread in  Virginia.  Other  States  in  which  the  disease  occurs  are  Arkansas, 
Connecticut,  Illinois,  Maryland,  Massachusetts,  Missouri,  Nebraska,  New 
Hampshire,  New  York  (particularly  Long  Island),  Rhode  Island,  and 
West  Virginia  (Scott  and  Rorer,  1908:48-49). 

Probably  no  apple  disease  except  apple  scab  is  commoner  in  New  York 
State  than  the  one  .  here  considered.  Throughout  western  New  York 
the  canker  form  is  very  prevalent.  From  replies  to  a  circular  letter  sent 
to  fruit  growers  in  various  parts  of  the  State,  it  appears  that  this  disease 
is  more  or  less  common  and  serious  in  all  sections,  except  possibly  in  the 
central  eastern  part.  The  fruit  and  foliage  rarely  suffer  apj^reciably  in 
the  State,  although  black  rot  and  leaf  spot  are  not  infrequently  found. 


58  Bulletin  379 

economic  importance 
general  considerations 

The  nature  of  the  losses  caused  by  this  disease  makes  very  difficult 
the  possibility  of  an  estimate  concerning  them.  So  far  as  the  writer  has 
found,  no  reliable  data  are  at  hand  in  regard  to  this  point.  The  com- 
bined injuries  produced  by  the  canker,  the  black  rot,  and  the  leaf  spot 
are  doubtless  greater  than  is  commonly  supposed.  It  is  undoubtedly  true 
that  the  New  York  apple  tree  canker  is  often  confused  with  other  cankers 
by  some  growers,  thus  increasing  the  difficulty  of  obtaining  reliable  esti- 
mates on  the  destructiveness  of  this  disease. 

It  is  generally  considered  that  canker  is  one  of  the  commonest  and 
most  troublesome  diseases  of  the  apple,  although  its  destructiveness  is 
not  uniform  in  different  parts  of  the  coimtry.  According  to  Shear  (1913 : 
81-82),  the  black  rot  disease  of  apple  is  found  in  Europe  from  Italy  to 
England;  yet  he  states  that  noticeable  injury  from  the  disease  in  orchards 
has  never  been  reported.  On  the  other  hand,  Griffon  and  Maublanc 
(1910:308)  state  that  in  France  the  injury  may  be  very  serious.  In 
contrast  to  the  general  situation  in  Europe,  it  may  be  noted  that  the 
damage  done  by  this  disease  in  America  is  great. 

NATURE  OF  LOSSES 

INJURY  TO  FRUIT.  Whenever  pome  fruits  are  attacked  they  are 
rendered  worthless  so  far  as  their  market  value  is  concerned.  The  extent 
of  injury  may  be  small  while  the  fruit  still  hangs  on  the  tree,  but  ultimately 
in  storage  complete  destruction  is  likely  to  result.  Brooks  (1909)  states 
that  in  New  Hampshire  the  black  rot  is  very  common  and  does  con- 
siderable damage  in  cellar  storage.  Burrill  and  Blair  (1901:2)  report 
"great  loss  at  times"  in  Illinois,  and  Clinton  (1902),  in  the  same  State, 
compares  the  importance  of  bitter  rot  and  black  rot  of  apple.  The  latter 
he  regards  as  likely  to  occur  in  every  orchard  to  some  extent.  In  Kentucky, 
black  rot  of  apples  is  regarded  as  the  commonest  of  fruit  rots,  according 
to  Garman  (1895:127).  Stone  (letter  to  the  writer)  estimates  that 
in  Massachusetts  from  eighty  to  ninety  per  cent  of  fruit  rots  is 
black  rot.  Evans  (1910)  reports  a  case  in  which  rotting  and  mummified 
pome  fruits  appeared  in  a  shipment  to  Cape  Colony,  and  states  in  this 
regard: 

During  the  past  three  months  four  hundred  and  ninety-eight  cases  of  apples  and 
pears  in  this  condition  from  Cape  Colony  have  been  detained,  and  in  order  to  safe- 
guard the  interests  of  Transvaal  fruit  growers,  the  Government,  under  Government 
Notice  No.  569,  of  i8th  June,  1908,  have  warned  importers  of  fruit  that  all  consignments 
of  pomaceous  fruits  found  infected  with  this  fungus  to  the  extent  of  one  per  cent  and 
upwards  will  be  destroyed  upon  arrival  in  this  Colony  or  returned  to  the  consignor. 

There  is  no  reason  to  suppose  that  this  number  by  any  means  represents  the  total 
amount  of  diseased  fruit  that  has  reached  the  Transvaal,  to  say  nothing  of  the  other 
parts  of  South  Africa. 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits      59 

INJURY  to  foliage.  The  damage  to  foliage  depends  on  the  extent  of 
the  infection.  In  the  milder  cases  the  injury  is  not  appreciable.  In  the 
more  severe  cases,  partial  or  even  complete  defoliation  may  occur  from 
six  weeks  to  two  months  before  the  ripening  of  the  fruit,  as  a  result  of  which 
the  fruit  either  drops  from  the  tree  or  remains  small  and  is  of  poor  quality. 
In  such  cases  the  fruit  buds  are  so  weakened  as  to  decrease  the  possibility 
of  a  crop  the  following  year,  and  the  vitality  of  the  trees  is  impaired. 
Alwood  (1892:62)  estimates  a  loss  of  seventy-five  per  cent  of  the  foliage 
in  a  part  of  an  old  orchard  in  Virginia,  while  Stewart  (1896)  reports  a 
case  of  complete  defoliation  of  some  trees  on  Long  Island  by  the  first  of 
July.  It  is  interesting  to  note,  for  comparison,  that  in  1900,  in  West 
Virginia,  the  disease  was  regarded  by  Corbett  (1900)  as  more  injurious  to 
foliage  than  either  blight  or  scab.  Scott  and  Rorer  (1909:10-11)  have 
observed  a  case  in  which,  as  they  believe,  the  pathogene  causing  this 
disease  assisted  in  the  killing,  in  late  summer,  of  a  large  proportion  of  the 
fruit  buds  of  the  apple.  They  state  that  on  Winesaps  it  would  seem 
the  pathogene  alone  is  capable  of  killing  the  buds.  Further  investigation 
is  deemed  desirable  by  these  writers. 

INJURY  to  limbs.  As  a  rule  the  canker  is  confined  to  the  orchard, 
although  Wilson  (19 13)  says  that  young  nursery  stock  may  be  killed. 
Bethune  (1909:28-29)  reports  that  cankers  cause  a  great  amount  of 
damage  in  Ontario,  Canada.  J.  W.  Eastham  (letter  to  the  writer),  of 
the  Ontario  Experiment  Farm,  states  that  this  is  the  most  prevalent 
canker  in  the  region  east  of  Toronto,  and  according  to  Brooks  (1909) 
it  is  the  commonest  canker  in  New  Hampshire.  Warren  and  McCourt 
(1905 :  341)  refer  to  this  form  of  the  disease  as  causing  more  loss  in  Wayne 
County,  New  Yorkf  than  any  other  disease  except  scab.  They  report 
it  as  very  serious  in  fourteen  per  cent  of  the  orchards,  and  as  doing  con- 
siderable damage  in  nineteen  per  cent  of  them.  In  Niagara  County, 
New  York,  Cummings  (1909:304)  found  canker  affecting  the  orchards  as 
follows:  slightly,  sixty-one  orchards;  considerably,  sixty -three;  seriously, 
thirty-seven.  Paddock  (1899  b:  181,  188)  cites  a  case  in  which,  in  an 
apple  orchard  of  80  acres,  the  trees  on  30  acres  were  ruined  and  had  been 
taken  out;  the  trees  on  the  remaining  50  acres  were  then  of  little  value. 

In  one  apple  orchard  of  three  hundred  and  fifty  trees  under  the  writer's 
observation,  a  count  made  in  August,  19 13,  showed  about  thirty-three 
per  cent  of  the  trees  (Baldwin,  Hubbardston,  and  Northern  Spy  varieties) 
with  from  one  to  three  dead  limbs  each.  On  examination  of  the  dead 
limbs  the  New  York  apple  tree  canker  was  found  to  be  present  on  all. 
It  was  further  observed  that  the  pathogene  causing  the  infection  had  lived 
over  winter  and  had  spread  to  such  an  extent  that  girdling  had  resulted 
and  the  foliage  had  turned  yellow  and  wilted.     The  fruit  on  such  limbs 


6o  Bulletin  379 

soon  shriveled  and  was  lost.  A  careful  count  showed  that  approximately 
ten  or  twelve  barrels  of  fruit  were  rendered  worthless.  The  loss  here 
might  be  placed  at  approximately  twenty  to  twenty-five  dollars,  or  about 
seven  cents  a  tree.  According  to  the  United  States  Census  for  19 10, 
there  were  in  New  York,  on  the  168,667  farms  reporting,  11,248,203  apple 
trees  of  bearing  age.^  On  this  basis,  assuming  the  losses  in  the  above- 
mentioned  orchard  to  be  an  average,  the  apparent  annual  loss  would  be 
about  three-fourths  of  a  million  dollars  for  a  single  season  in  New  York 
State.  Many  cases  can  be  cited  in  which  the  infection  by  New  York  apple 
tree  canker  is  very  much  more  severe,  while  few  orchards  in  the  State, 
regardless  of  their  careful  management,  are  entirely  free  from  the  disease. 
Epiphytotics  of  this  disease,  such  as  have  recently  been  experienced  in 
the  case  of  the  chestnut  blight,  are  of  rare  or  unknown  occurrence.  It  is 
characteristic  of  the  disease  to  take  a  constant  toll  year  after  year,  like  the 
cereal  smuts.  To  the  losses  so  incurred  must  be  added  the  cost  of  growing 
diseased  limbs.  In  many  cases  these  limbs  die,  resulting  in  the  cost  of  their 
removal  and  destruction,  which  possibly  does  not  seem  great  in  a  given 
year  but  is  not  negligible  in  the  aggregate. 

SYMPTOMS 
ON  THE  FRUIT 

The  disease  on  the  fruit  is  primarily  a  ripe  rot,  but  it  may  appear  several 
weeks  before  maturity  of  the  fruit.  It  may  begin  anywhere  on  the  surface 
or  at  the  blossom  end.  Frequently  the  lesions  are  centered  about  an 
injury  such  as  that  caused  by  insects  or  hail  (Plate  vii,  i). 

Usually  there  is  only  one  spot  on  a  fruit.  The  skin  at  first  becomes 
brown  in  a  small  area,  but  later  darkens,  finally  turning  black.  On  green 
fruit  the  affected  part  may  turn  black  before  enlarging  to  any  great  extent, 
whereas  on  fruit  that  is  ripe  or  ripening,  the  whole  may  be  involved  before 
it  darkens  appreciably.  Often  concentric  bands  of  uniform  breadth  and 
of  slightly  different  shades  of  color  appear  about  the  center  of  the  lesion. 
The  affected  area  is  distinct  from  the  healthy  part,  and  the  diseased  tissues 
are  not  of  unpleasant  taste  as  in  many  fruit  decays.  Later  stages  in  the 
development  of  the  rot  show  a  shriveled  and  much  wrinkled  surface,  which 
typically  becomes  covered  with  black  pustules  (Plate  vii,  2).  These  char- 
acters may  be  assumed  within  a  month  or  in  less  time.  Ultimately  a  dry 
mummy  is  produced,  which  may  hang  to  the  tree  for  a  year  or  more. 

Black  rot  has  been  confused  with  brown  rot  and  bitter  rot,  and  even  with 
soft  rot.  The  brown  rot  disease  produces  a  smooth,  coal  black,  and  shiny 
mummy,  which  is  much  less  wrinkled  than  the  black  rot  mummy.  Bitter 
rot,  in  addition  to  its  unpleasant  taste,  often  shows  pinkish  specks  in  a 


3  Bureau  of  the  Census.     Thirteenth  Census  of  the  United  States  taken  in  the  year  1910,  7  :  195. 


I        Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits      6i 

localized  region  near  the  center  of  the  lesion.  The  softening  of  the  pulp 
in  soft  rot  is  not  characteristic  of  black  rot  specimens.  Perhaps  the  most 
distinctive  characters  of  black  rot  are  the  long  duration  of  the  plumpness 
and  juiciness  of  the  tissues,  and  the  occurrence  of  the  above-mentioned 
black  pustules.  Under  certain  conditions  the  surface  of  the  apple  fruit 
also  becomes  studded  with  white  tufts;  but  these  are  not  commonly 
found  and  are  not  to  be  regarded  as  a  diagnostic  symptom. 

Fruits  of  the  pear  and  the  quince  affected  with  black  rot  finally  become 
dry  and  hard.  In  storage  the  peach  becomes  waxy  when  affected  with 
the  disease,  according  to  Baccarini  (1890:67). 

ON  THE  LEAVES 

The  foliage  of  tne  apple  is  more  frequently  attacked  than  that  of  the 
pear  and  the  quince.  The  spots  usually  appear  about  the  time  the  leaves 
open.  Alwood  (1892  :  62)  notes  this  date  as  being  about  May  i  in  Virginia. 
He  records  a  second  attack  which  becomes  evident  about  June  20,  and  a 
third  outbreak  the  last  of  July.  Brooks  and  DeMeritt  (1912:181)  state 
that  in  New  Hampshire  apple  leaf  spot  appears  soon  after  the  leaves 
unfold  from  the  bud.  In  western  New  York  spotting  is  more  commonly 
apparent  in  July  and  August.  The  writer  observed  spots  developed  in 
September,  19 13,  at  Byron,  New  York. 

The  number  of  lesions  that  may  appear  on  a  single  leaf  varies  from  one  to 
several,  and  these  may  be  scattered  or  localized  on  the  surface  (Plate  vii,  3). 
The  first  evidence  of  a  spot  is  a  minute  purple  speck,  which  soon  enlarges 
until  it  has  reached  a  diameter  of  from  two  to  ten  millimeters,  averaging 
about  four  millimeters.  The  purplish  color  is  maintained  for  a  con- 
siderable time,  during  which  the  margin  is  somewhat  indefinite.  Later  the 
lesion  is  of  a  yellowish  brown  color  and  the  spot  assiimes  a  more  or  less 
circular  shape,  while  the  margin  becomes  more  definite.  Still  later  the 
margin  becomes  elevated  and  the  diseased  area  sunken.  As  the  spots 
grow  older  they  become  lobed,  due  to  a  secondary  extension  of  the  patho- 
gene  from  one  or  more  points,  and  finally  a  series  of  more  or  less  concentric 
areas  produces  an  irregular  blotch  in  which  the  outline  of  the  original 
spot  can  be  recognized.  The  center  has  now  become  grayish  brown,  and 
the  entire  lesion  presents  an  appearance  which  has  given  rise  to  the  name 
frog-eye. 

The  spots  on  the  lower  surface  seem  to  enlarge  as  rapidly  as  those  on 
the  upper,  but  they  are  not  so  conspicuous.  Sometimes  the  center  of 
the  spot  on  the  lower  surface  is  grayish  brown.  The  whole  diseased 
area  may,  however,  merely  appear  dark  and  indefinite. 

Frequently  small,  black,  dome-like  bodies  are  found  on  the  upper  surface 
of  the  leaf,  usually  toward  the  center  of  the  lesion.     In  severe  cases  the 


62  Bulletin  379 

leaves  turn  yellow  and  fall  from  the  tree.  According  to  Brooks  and 
DeMeritt  (1912:181),  this  leaf  fall  occurs  from  six  to  eight  weeks  earlier 
than  would  happen  normally.  Reed,  Cooley,  and  Rogers  (1912:3) 
maintain  that  defoliation  may  occur  early  enough  for  a  new  crop  of 
leaves  to  be  put  forth  the  same  season.  Trees  robbed  of  their  foliage 
from  year  to  year  must  eventually  become  greatly  reduced  in  vitality 
and  finally  succtraib  to  a  premature  death. 

Bordeaux  injury  is  sometimes  very  similar  to  frog-eye  leaf  spot;  Brooks 
and  DeMeritt  (1912:190)  state  that  this  is  especially  true  if  rains  follow 
the  application.  Kinney  (1895  b)  notes  also  that  injuries  from  the 
leaf  miner  {Tischeria  malifoliella  Clemens)  are  sometimes  mistaken  for 
leaf  spot. 

ON  THE  LIMBS 

In  western  New  York,  young  spots  may  be  found  on  the  bark  at  any 
time  from  the  last  of  April  until  toward  the  close  of  the  growing  season. 
Numerous  young  cankers  have  been  observed  on  Twenty  Ounce  trees 
in  Monroe  County  orchards  during  the  month  of  August.  It  is  the 
rule  that  the  larger  limbs  are  much  more  susceptible  than  the  twigs, 
and  the  trunks  show  comparatively  few  lesions.  The  cankers  on  the 
trunks  occur  more  or  less  uniformly  on  the  southwest  side  of  trees.  The 
limbs  more  commonly  show  the  diseased  spots  on  the  upper  side.  Lesions 
are  very  often  found  about  the  base  of  a  small  limb  or  about  a  wound 
in  the  bark. 

In  the  earlier  stages  of  the  formation  of  a  canker,  the  bark  is  slightly 
sunken  (Plates  viii,  and  ix,  4)  and  reddish  brown  in  color.  The  diseased 
area  slowly  increases  in  size  and  darkens,  and,  although  not  conspicuous 
at  a  distance,  the  spot  is  readily  distinguished  from  healthy  tissue  on  closer 
examination.  Some  lesions  remain  very  small,  measuring  only  a  few  centi- 
meters in  their  longer  diameter;  in  such  cases  the  canker  usually  dies 
out  at  the  end  of  the  year.  Where  the  injury  is  larger,  the  diseased 
spot  enlarges  from  year  to  year  for  a  distance  of  a  meter  or  even  more. 

It  is  often  observed  that  a  canker  is  merely  a  superficial  roughening 
of  the  bark.  In  other  cases  the  bark  is  killed  to  the  wood  and  becomes 
conspicuously  cracked  (Plate  x). 

The  discolored  area  may  extend  over  a  considerable  surface;  or,  regard- 
less of  its  size,  a  crevice  may  appear  at  the  margin,  limiting,  temporarily 
at  least,  the  extent  of  the  lesion.  Further  spread  of  the  pathogene  results 
in  the  formation  of  a  prominent  spot,  which  soon  forms  a  second  line 
of  demarcation  between  the  healthy  and  the  diseased  tissue.  Repetition 
of  this  process  from  one  or  more  points  at  the  margin  occurs,  thus  pro- 
ducing a  lobed  appearance  (Plate  xi,  2);  or  the  spreading  may  arise  from 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits      63 

all  points  about  the  first  marginal  crack,  so  that  a  series  of  concentric 
crevices  is  developed,  as  described  for  frog-eye  of  the  leaves.  The 
bark  remains  closely  appressed  to  the  wood  for  at  least  a  year;  later 
the  dead  bark  cracks  and  falls  away,  exposing  the  wood  and  a  callus  around 
the  margin  of  the  wound  (Plate  x,  3). 

Cankers  that  begin  to  form  early  in  the  season  show  numerous  fruit- 
ing pustules  of  the  pathogene  scattered  over  the  central  area  of  the  spot. 
These  may  not  become  evident,  however,  until  the  second  season. 

Large  limbs  are  rarely  girdled  the  first  year;  the  girdling  comes  about 
by  the  enlargement  of  the  canker  the  following  season.  Complete  encircling 
results  in  the  death  of  the  parts  above  the  canker,  as  evidenced  by  the 
yellowing  and  dropping  of  the  leaves  (Plate  xii,  i)  and  the  shriveling  of  bark 
and  fruit.  It  is  not  uncommon  in  such  cases  to  find  the  fruit  clinging 
to  the  twigs  for  a  year  or  more. 

Clinton  (1907)  describes  a  peculiar  type  of  lesion  on  apple  limbs.  He 
says,  in  part: 

Another  and  more  peculiar  feature  of  the  trouble  was  the  enlargement  of  the  limbs 
into  somewhat  fusiform  swellings,  as  shown  in  the  illustration.  In  some  cases  several 
of  the  swellings  followed  one  another  on  the  same  limb.  These  enlargements  generally 
showed  a  greater  swelling  on  one  side  than  on  the  opposite,  and  often  the  bark  was 
split  down  the  more  swollen  side.  Cross  and  longitudinal  sections  showed  that  the 
swellings  were  apparently  the  result  of  severe  cold,  which  had  injured  the  limbs  unevenly 
along  the  branch,  as  shown  by  the  blackened  wood  on  the  injured  portion. 

Delacroix  (1903 a:  135)  notes  a  thickening  at  the  base  of  some  cankers. 
This  he  finds  to  be  a  sort  of  cushion  developed  in  a  transverse  direction 
in  the  healthy  bark.  The  writer  has  occasionally  observed  cankers 
showing  hypertrophy  at  the  upper  and  lower  ends  of  the  diseased  part 
(Plate  X,  4). 

It  is  to  be  noted  that  on  quince  twigs  the  cankers  are  often  very  indefinite. 
A  rare  specimen  is  shown  in  Plate  x,  5.  The  normal  color  of  the  bark 
is  not  distinctly  lighter  than  that  of  the  diseased  part,  so  that  on  this 
host  the  disease  doubtless  passes  unnoticed  in  many  cases. 

OTHER  organs  AFFECTED 

A  unique  case  in  Virginia  of  fall  blossoming  of  the  apple  following 
the  canker  has  been  described  by  Reed  (1908).  This  author  found  normal 
blossoms  on  an  apple  tree  in  the  orchards  of  the  Virginia  Experiment 
Station  on  October  5.  The  cankers  on  the  limbs  had  caused  the  death 
of  more  than  half  the  top  of  the  tree,  and  many  branches,  severely  affected, 
had  been  able  to  make  a  very  small  amount  of  growth  during  the  season. 
Reed  says:  "  It  was  on  such  branches  as  these  that  fruit  buds  were  found 
open  on  the  above  named  date.  Examination  of  the  blossoms  showed 
that  they  were  normal  as  regards  parts,  color,  and  internal  relationships. 


64 


Bulletin  379 


I  am  informed  by  Professor  H.  L.  Price  of  the  Department  of  Horticulture 

of  this  Experiment  Station  that  this  fall  blossoming  is  not  uncommon 
on  trees  which  are  badly  affected  by  the  black  rot  fungus." 


ETIOLOGY 

The  pathogene  here  concerned  is  the  fungus  Physalospora  Cydoniae 
Arnaud. 

MORPHOLOGY 

PERiTHECiA.  The  perithecia  have  been  found  by  the  writer  on  the 
twigs  of  apple  {Pyrus  malus  L.)  and  of  witch-hazel  {Hamamelis 
virginiana  L.),  and  have  been  described  by  him  in  another  publication 


OG 


^^ 


Fig.  18.      PERITHECIUM  OF  PHYSALOSPORA   CYDONIAE 

Camera  lucida  drawing  of  a  median  longisecuon  ot  a  typical  perithecium 

(Hesler,  1913:293).  Recently  the  writer  has  found  the  ascogenous  form 
on  twigs  of  white  oak  {Quercus  alba  L.). 

The  perithecia  are  usually  scattered,  standing  separate  from  one  another. 
Sometimes,  however,  from  two  to  four  fruit  bodies  are  joined  together, 
but  no  stroma  has  ever  been  observed.  They  are  buried  in  the  cortical 
tissues,  protruding  at  maturity  by  a  short,  papillate  ostiole.  Their 
form  is  globose  to  svibglobose,  measuring  from  180  to  324 /x  in  the  vertical 
diameter  by  300  to  400  u  in  the  horizontal  diameter,  averaging  about 
225  by  325M- 

A  typical  perithecium  is  shown  in  figure  18.  The  wall  is  differentiated 
into  two  layers.  The  thickness  of  the  outer  layer  varies  slightly  with 
the  sides  and  base  of  the  perithecium,  and  the  pseudo-cells  are  thick- 


Bulletin  379 


Plate  VII 


t 


lb 


SYMPTOMS  OF  THE  DISEASE  ON  FRUIT  AND  FOLIAGE 

1.  Types  of  infection  on  apples,  early  stages 

2.  Apples  reduced  to  mummies  as  a  result  of  the  disease 

3.  Types  of  infection  on  apple  leaves  as  commonly  found  m  New  York  btate 


Bit. LETT \  379 


Plate  IX 


NATURAL    CANKERS    AND     CANKERS    PRODUCED    BY    ARTIFICIAL     INOCULATION    WITH 
FHYSALOSPORA  CYDONIAE 

1.  Natural  infection  on  the  left;  artificial  infection  on  the  right.  The  latter  inoculated  on  July  r, 
1913,  with  a  strain  from  Twenty  Ounce  apple  bark.     Photograph  made  September  30,   1913 

2.  Canker  on  trunk  of  mature  pear  tree.  Inoculation  made  July  18,  1910,  photograph  made 
September  i,  191 1 

3.  The  result  of  inoculation  by  use  of  pycnospores  from  apple  leaves.  The  healing  process  has 
occluded  the  wound  before  the  pathogene  could  produce  a  large  canker.  Inoculation  made  July  i, 
1912,  photograph  made  September  20,  1913 

4.  Canker  on  Baldwin  twig  produced  artificially,  using  ascospores  from  apple.  Inoculation  made 
July  25,  1914,  photograph  made  December  10,  1914 


Bulletin  379 


Plate  XI 


INOCULATION  EXPERIMENTS  WITH  PHYSALOSPORA  CYDONIAE 

1.  The  three  cankers  on  the  left  produced  by  inoculating  pear  with  ascospores  from  apple. 
Check  on  the  right.     Inoculations  made  June  6,  1913.  photograph  made  September  20,  1913 

2.  Canker  on  Twenty  Ounce  limb  produced  artificially,  using  pycnospores  from  apple. 
Inoculation  made  June  20,  19 12,  photograph  made  September  20,  19 13 

3.  Canker  produced  on  pear  by  inoculation  with  ascospores  from  apple.  The  presence 
of  pycnidia  should  be  noted.  Inoculation  made  June  6,  1913.  photograph  made  September 
20,  1913 


Bulletin  379 


Plate  XII 


NEW  YORK  APPLE  TREE  CANKER 

1.  Twenty  Ounce  apple  tree,  some  of  the  larger  limbs  of  which  have  been  girdled  by  the  fungus. 
Evidence  that  this  has  occurred  is  found  in  the  defoliated  tops  of  affected  limbs 

2.  External  view  at  left,  and  internal  view  at  right,  of  young  black  rot  lesions  on  apple;  the  specimen 
on  the  right  shows  the  tissues  involved 


Bulletin  379 


VARIOUS  STAGES  OF  PHYSALOSPORA  CYDONIAE 

1.  Showing  differences  in  growth  on  nutrient  a^ar  from  pycnospores  (heavy  dark  growth  on  left) 
and  from  ascospores  (scant  growth  on  right) 

2.  Photomicrograph  of  asci,  ascospores,  and  paraphyses  from  a  single  perithecium 

3.  Sclerotia  as  they  appear  in  pure  culture 

4.  Twig  of  apple,  showing  dark  masses  of  pycnospores  which  have  oozed  from  the  pycnidia  when 
the  twig  was  kept  in  a  moist  chamber 


Bulletin  379 


INOCULATION  EXPERIMENTS  WITH  PHYSALOSPORA  CYDONI.E 

1.  Canker  on  right,  check  on  left.  Inoculation  made  July  i,  1912,  using  pycnospores 
from  pear,  the  fungus  having  followed  fire  blight.      Photograph  made  September  20,  1913 

2.  Comparison  of  two  different  apple  strains  on  pear.  Specimen  shown  on  left  inoculated 
with  ascospores  from  apple.  Specimen  shown  in  center  inoculated  with  pycnospores  from 
apple,  following  fire  blight.  The  very  slight  infection  should  be  noted.  Check  on  right. 
Inoculation  made  June  6,  1913.  photograph  made  September  20,  1913 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits       65 


walled.  The  inner,  thin-walled  layer  is  of  very  uniform  diameter.  In 
cases  in  which  the  perithecium  is  depressed,  the  outer  layer  is  reduced 
at  the  base  and  is  from  one  to  three  pseudo-cells  in 
thickness,  whereas  the  lateral  outer  walls  are  from  two 
to  five  layers  of  pseudo-cells  in  thickness.  The  ostiole 
appears  as  a  narrow  passage  in  the  papilla,  the  walls 
of  which  show  the  same  distinct  layers  as  those  just 
described  for  the  sides  and  base  of  the  perithecium. 

The  asci,  with  the  interspersed  paraphyses,  usually  fill 
the  cavity  of  the  perithecium.  Arnaud  (1912 :  11)  states 
that  in  general  the  paraphyses  are  formed  by  rows  of 

cells  which 
in  the  ma- 
ture peri- 
thecium 
are  sepa- 
rated one 
from  an- 
other    in 


Fig.  19.     ASCI  and 

PARAPHYSES  OF 
PHYSALOSPORA 
CYDONIAE 

Camera  lucida  draw- 
ing of  asci  and  paraph- 
yses,  showing  structure 

thp  form  nf    °^  *^^  '^"'^''  ^"'^  typical 
Cne  lOrm  01    arrangement     of    asco- 

distinct  fil-  'P""""  '"  ^^"^  ^'="' 
aments.  He  says  that  in  cer- 
tain cases,  however,  the 
paraphyses  remain  aggluti- 
nated by  their  walls  and 
appear  in  section  like  rows  of 
cellular  cavities,  as  in  Cucur- 
bitaria  (C.  Spartii  and  other 
species) .  He  explains  that  if 
the  rows  of  cells  are  not  very 
nimierous  the  existence  of  the 
paraphyses  may  become  un- 
certain. Arnaud  finds  this 
the  case  with  Physalospora 
Cydoniae.  The  writer,  how- 
ever, has  not  observed  this 
ASCI  OF  PHYSALOSPORA  CYDONIAE  FROM  condition  of  the  paraphyses ; 

The  upper  series  r^entfJarfaSL' as  found  on  apple    ^°    ^'"^   ^^^^   ^PP^^^    ^^^^^"^^ 
bark.    The  lower  series  shows  variations  from  bark  of  witch-     and  nOn-SCptatC    (Fig.    lo). 

The  asci  are  abundant; 
asci  crushed  from  one  perithecium  are  shown  in  Plate  xiii,  2.  They  are 
usually  clavate,  although  they  sometimes  tend  to  be  cylindrical,  measuring 


20. 


66 


Bulletin  379 


Fig. 


PHY- 


from  21  to  32  /J  b>  130  to  180  /x.     The  tip  of  the  ascus  is  thickened,  but  a 
complete  canal  from  the  inner  wall  to  the  outside  has  not  been  observed; 

only  a  suggestion  of  such  a  canal 
has  been  seen  even  after  the  peri- 
thecia  had  been  kept  in  a  moist 
chamber  for  several  hours.  Varia- 
tions of  asci  from  different  hosts  are 
shown  in  figure  20. 

The  ascospores  are  ellipsoidal,  or 
often  inequilateral  (Fig.  21);  they 
measure  from  10.8  to  15.2 /z  by  23.4 
to  34.2 /x,  averaging  11. 5  by  28 /x. 
They  are  hyaline  to  greenish  yellow. 
Under  ordinary  conditions  the  spores 
show  a  very  thin  gelatinous  sheath, 
but  after  they  have  been  in  a  satu- 
rated atmosphere  for  a  few  hours  the 
sheath  becomes  very  broad  and  evi- 
dent. The  arrangement  of  the  spores 
in  the  ascus  is  more  or  less  biseriate. 
The  paraphyses  are  distinct  and  are 
occasionally  branched  near  the  tip. 
Not  infrequently  the  apex  shows  a  tendency  to  be  clavate. 

The  number  of  spores  in  each  ascus  is  typically  eight,  but  exceptions 
have  been  found  in  the  fungus  on  apple  twigs.  The  variation  ranges  from 
two  to  eight  spores  within  an  ascus,  all  intervening  numbers  having  been 
observed.  Four-spored  asci  are  not  uncommon  (Fig.  20).  The  contents 
of  ascospores  are  either  densely  granular,  or  vacuolate  and  oily.  Two 
guttules  are  occasionally  found. 

PYCNiDiA.  The  morphology  of  the  pycnidial  form  of  this  fungus  is 
variable  (Fig.  22).  The  pycnidia  are  situated  in  the  cortical  tissues 
and  are  usually  scattered  and  distinct,  although  on  the  same  organ  of 
the  host  they  may  be  single,  confluent,  or  united  into  a  stroma.  The 
number  of  pycnidia  per  unit  of  area  is  usually  less  on  woody  substrata 
than  on  fruits ;  on  apple  fruit  there  may  be  from  one  hundred  and  twenty 
to  one  hundred  and  fifty  pycnidia  per  square  centimeter. 

The  typical  simple  pycnidium  (Fig.  22,  a)  measures  from  200  to  300  fx 
in  each  diameter,  whereas  the  compound  fruit  body  may  vary  from  200 
to  460  ;u  in  the  vertical  diameter  and  from  200  to  720/1  in  the  horizontal 
diameter  (Fig.  22,  g).  Their  shape  is  in  general  the  same  as  that  of  the 
perithecia,  globose  to  subglobose,  and  they  have  the  same  distinct  outer 
and  inner  walls.     The  thickness  of  the  entire  pycnidial  wall  is  variable, 


:i.   TYPES  OF  ASCOSPORES 
SALOSPORA  CYDONIAE 

A,  Typical  mature  ascospores  as  found  in  nature; 
B.  ascospores.  showing  stages  in  the  development  of 
the  gelatinous  sheath;  C,  old  ascospores,  showing 
peculiar  contents 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits       67 


as  in  the  case  of  the  perithecium.  The  basal  part  is  thinner  in  the  case 
of  the  subglobose  fruit  bodies.  This  condition  may  be  attributed  to  the 
fact  that  less  protection  is  needed  at  the  base;  or  perhaps  here  the  thick- 
ness may  be  partially  determined  by  mechanical  pressure  brought  about 
by  the  resistance  offered  by  the  host  tissue. 

Arising  from  the  inner  thin-walled  cells  are  the  pycnosporophores,  which 


_  Fig.  22.      VARIATIONS  OF  PYCNIDIA  OF  PHYSALOSPORA  CYDONIAE 

A,  Typical  simple  unilocular  pycnidium;  B,  pycnidium  with  long  neck,  similar  to  C  but  with  an  ostiolum; 
C,  pycnidium  similar  to  B,  ostiolum  not  yet  developed;  D,  pycnidium  from  apple  leaf;  E,  hair-like  out- 
growths on  the  tip  of  an  ostiolum,  developed  under  moist  conditions;  F,  pycnidium  with  mound-like  struc- 
ture at  base;  G,  pycnidium  which  approaches  in  appearance  the  fruiting  body  of  species  belonging  to  the 
form-genus  Botryodiplodia 

extend  entad.  They  are  clavate,  flask-shaped,  or  cylindrical.  They  may 
be  as  long  as  the  spore  itself,  from  25  to  30 /x,  or  may  measure  less  than 
8/x;  the  average  dimensions  are  from  10  to  15  /i  by  3  to  4 /x.  At  the  tip 
of  each  is  developed  a  pycnospore. 

In  some  cases  there  is  a  mound-like  structure  at  the  base  of  the  pycnidium 
(Fig.  22,  f).  This  is  illustrated  byDuggar(igo9:353,fig.  171).  It  has  been 
a  matter  of  conjecture  whether  this  may  appear  only  in  an  oblique  tan- 


68  Bulletin  379 

gential  section,  or  whether  it  is  a  bilocular  tendency.  It  does  not  seem 
possible  that  any  such  structure  would  appear  merely  in  a  section  that 
was  not  cut  vertically.  If  this  were  true,  the  question  would  then  arise 
as  to  whether  this  same  appearance  would  not  extend  at  all  points  along 
the  lining  of  the  cavity,  and  hence  merely  make  the  wall  thicker  rather 
than  give  it  the  aspect  just  described.  It  seems,  therefore,  to  be  a 
bilocular  tendency. 

Frequently  the  pycnidium  approaches  and  even  reaches  the  condition 
characteristic  of  the  form -genus  Botryodiplodia  (Fig.  22,  g).  The  sporog- 
enous  layer  extends  inward  at  places,  giving  the  inner  wall  a  corrugated 
appearance.  This  condition  is  found  in  nature  and  has  been  developed 
in  culture  from  spores  in  pycnidia  which  originally  did  not  show  this 
structure.  The  simplest  condition  suggesting  the  form-genus  Botryodi- 
plodia is  found  when  a  single  mound-like  structure  occurs  at  the  base  of 
the  pycnidium,  as  previously  described  (Fig.  22,  f).  Frequently  this  finds 
its  expression  in  the  form  of  a  bilocular  condition,  which  is  a  step  nearer 
the  Botryodiplodia  type. 

The  ostiolum  offers  some  interesting  variations.  Miss  Walker  (1908) 
describes  a  form  which  she  believes  lacks  an  ostiolum.  In  the  place  of 
the  typical  conical  ostiolate  neck  there  was  found  a  much-thickened  wall 
at  the  apex  of  the  fruiting  body,  and  the  papilla  itself  appeared  longer 
than  usual.  The  writer  has  cultured  the  ostiolate  form  from  an  apple, 
and  has  obtained,  on  various  agars  and  on  apple  fruit,  pycnidia  having 
the  characteristics  described  by  Miss  Walker  (Fig.  22,  c) .  The  evidence  at 
hand  indicates  that  a  pore  may  or  may  not  be  present,  depending  some- 
what on  the  time  of  year  and  on  weather  conditions.  In  any  case  an 
ostiolum  will  ultimately  be  developed  (Fig.  22,  a,  b,  d).  Brooks  and  De 
Meritt  (191 2  :  184)  report  three  types  of  pycnidia  but  all  forms  are  ostiolate. 
It  does  not  seem  likely  that  any  strain  will  remain  void  of  an  ostiolum 
throughout  its  history.  A  strongly  papillate  form  similar  to  that  shown 
in  figure  22,0,  but  with  an  ostiole  developed,  is  illustrated  in  figure  22,  e. 
A  form  of  the  fungus  which  at  first  appeared  to  have  a  non-erumpent 
pycnidium  was  found  in  apple  bark  and  twigs  of  Cclastrus  scandens  L. 
After  the  material  had  been  in  a  moist  chamber  for  a  few  days,  however, 
the  pycnidia  broke  through  the  epidermis. 

In  conclusion  it  may  be  stated  that  the  pycnidia  may  vary  in  mor- 
phology on  different  host  plants,  yet  this  variation  is  no  greater  than  that 
on  the  same  host  plant. 

PYCNiDiAL  FORMATION.  The  pycuidia  arise  from  the  mycelium  and  are 
found  abundantly  on  cankers  and  decayed  fruit.  Also  they  may  be 
produced  on  various  artificial  media.  They  occur  sparingly  on  spotted 
leaves. 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits 


69 


So  far  as  has  been  determined,  the  process  of  formation  is  similar  on 
different  substrata.  The  earher  stages  are  more  accurately  followed 
in  agar  cultures  than  on  any  organs  of  the  host  plant.  The  writer's  obser- 
vations have  been  made  by  examining  petri-dish  cultures  under  the  low 
power  of  the  microscope  and  by  the  use  of  prepared  slides  from  such 
cultures  The  material  was  prepared  as  follows:  Pycnospores  or  hyphal 
threads  were  planted  in  the  center  of  agar  plates,  and,  as  the  hyph^ 
developed,  pycnidia  appeared  in  more  or  less  definite  concentric  rings. 
In  this  way  the  oldest  pycnidia  were  nearest  the  starting  point,  whereas 
the  youngest  were  found  near  the  margin  of  the  culture,  the  stages  between 


Fig.  23.   DEVELOPMENTAL  STAGES  OF  THE  PYCNIDIUM 

A    Early  stage  in  pycnidial  development.     The  hypha;  have  become  closely  ^ePt^^^^^' .^^^^l^^t'^t^te; 

process  of  pycnidial  formation 

the  two  being  intermediate.  Blocks  of  agar  were  cut  out  from  the  dish, 
fixed,  and  imbedded  in  paraffin.  A  single  section  frequently  includes 
a  gradual  series  of  the  several  stages,  from  the  very  youngest  to  the  more 
mature  structures.  The  sections  were  made  both  perpendicular  and 
parallel  to  the  surface  of  the  agar,  the  second  method  proving  the  more 
satisfactory. 

The  young  pycnidium  as  it  occurs  in  agar  appears  to  be  made  up  of 
a  closely  tangled  mass  of  hyphas.  In  section  the  young  fruiting  body 
is  composed  of  pseudoparenchyma,  the  cells  of  which  are  closely  packed 
and  consequently  somewhat  angular  (Fig.  23,  h) .  As  is  noted  by  De  Bary 
(1887 :  247),  pycnidia  may  arise  either  as  intercalary  formations  on  hyphal 
branches  by  the  swelling  and  division  of  cells,  or  by  the  union  and  inter- 


70  Bulletin  379 

weaving  of  mycelial  threads.  The  former  process  is  termed  meristogenetic 
and  the  latter  symphyogenetic.  A  third  possible  method,  not  unknown 
among  the  fungi,  is  by  a  combination  of  these  two  processes. 

Potebnia  (1910:62),  in  a  note  on  Sphaeropsis  pseudodiplodia  (Fckl.) 
G.»  Del.,  states  that  the  pycnidia  arise  meristogenetically.  The  writer 
was  for  some  time  under  the  impression  that  this  was  the  character  of 
the  process,  but  this  opinion  was  based  on  observations  of  later  stages 
rather  than  on  the  earliest  steps  in  the  development.  The  dense  pseudo- 
parenchyma  of  the  maturer  fruit  bodies  suggests  meristematic  divisions, 
but  apparently  the  structure,  for  the  most  part,  arises  symphyo- 
genetically  (Fig.  23). 

In  agar  cultures  a  group  of  threads  may  be  observed  to  be  directed 
toward  a  common  point  where  the  pycnidium  is  to  be  formed.  Here 
the  hyphee  are  composed  of  cells  from  6  to  7  ju  broad,  their  length  varying 
from  20  to  70 /i,  always  longer  than  broad.  In  the  region  where  the 
pycnidiym  is  to  be  developed,  the  cells  become  noticeably  shorter  by 
the  laying  down  of  new  walls;  the  cells  also  increase  in  diameter  by 
growth,  and  the  hyphse  increase  their  numbers  by  branching  (Fig.  23, a). 
This  stage  is  observed  with  ease  in  petri-dish  cultures. 

The  behavior  of  the  threads  in  the  formation  of  the  pseudoparenchyma 
is  varied  and  the  process  is  somewhat  indefinite.  The  mycelial  branches 
that  enter  into  the  structure  may  arise  from  the  short  cells  (Fig.  23,  a),  or 
they  may  grow  in  from  adjacent  hyphae  (Fig.  23,  e).  The  interspaces 
found  in  the  earlier  stages  are  filled  by  the  growing  in  of  these  branches 
and  by  a  budding-like  action  of  the  hyphal  cells  bordering  the  space 
(Fig.  23,  b). 

Serial  sections  show  that  there  is  considerable  coiling  and  gnarling 
of  hyphas.  Threads  may  twist  about  one  another  for  some  distance 
in  a  rope-like  fashion  (Fig.  23,  d).  In  some  cases  the  threads  are  localized 
in  their  intertwining  so  that  the  resulting  structure  becomes  a  knot  or 
ball  of  densely  woven  hyphse  (Fig.  23,  f,  g,  h  ).  The  formation  of  such  a 
structure  necessitates  that  the  hyphse  pass  into  many  planes,  and  in  cross 
sections  the  ends  of  many  hyphse  present  a  pseudoparenchymatous  appear- 
ance (Fig.  23,  h). 

In  the  intertwining  process,  hyphse  may  conjugate  in  an  H-shaped 
fashion.  In  some  cases  threads  that  are  parallel  probably  fuse  side  by  side, 
although  the  evidence  for  this  is  not  complete. 

The  next  important  stage  is  the  formation  of  the  cavity.  At  first 
no  differentiation  of  the  closely  tangled  mass  of  threads  is  shown  in  the 
young  pycnidium,  but  soon  the  preparation  for  the  cavity  is  evident. 
Certain  cells  occupying  the  central  region  become  more  densely  granular 
than  the  surrounding  cells.     This  appears  to  be  the  beginning  of  the 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits       71 

cavity.  Later  stages  show  the  breaking  down  of  these  cells,  and  finally 
an  oval  or  a  globose  cavity  is  formed.  Baccarini  (1890:69)  states  that 
these  central  cells  transform  by  a  mucilaginous  process,  and  that  the 
cavity  is  enlarged  by  the  gelatinous  center's  absorbing  water  and  exerting 
a  pressure  on  the  sporogenous  layer.  He  emphasizes  the  importance 
of  the  central  "tissue"  and  expresses  the  opinion  that  it  has  a  special 
function,  believing  that  it  is  destined  to  become  sporogenous  whereas 
the  outer  surrounding  cortex  only  furnishes  nourishment  to  these  cells. 

The  formation  of  the  ostiole  is  similar  to  the  process  exhibited  by  the 
development  of  the  cavity.  The  cells  break  down,  enlarging  the  passage, 
and  finally  the  wall  is  definite  and  continuous  with  that  of  the  spore  cavity. 

The  spore-bearing  area  occupies  almost  all  the  space  not  included 
by  the  ostiole.  The  cells  lining  the  cavity 
arch  outward,  and  continued  growth  results 
in  the  formation  of  a  stalk.  The  tip  of  the 
stalk  swells,  and  ultimately  a  mature  spore  is 
cutoff  (Fig.  24).  The  further  development 
of  the  pycnospores  has  been  discussed. 

pygngspores.  The  morphology  of  the  ^'i^- ^4-  pycnospore  devel- 
pycnospores  has  been  more  carefully  studied  stages  in  the  formationof  a  pycno- 
than  that  of  the  pycnidia.  In  the  same  and  ^po- ^^o^  -  comdiophore 
in  different  pycnidia  on  the  same  and  on  different  plants,  wide  variation 
with  respect  to  size,  color,  shape,  and  septation  have  been  observed 
(Fig.  25). 

The  average  mature  pycnospore  measures  about  12  by  25 /x,  although 
the  range  in  single  or  in  different  pycnidia  on  the  same  or  on  different 
hosts  or  host  parts  may  be  considerable.  From  the  measurement  of 
hundreds  of  pycnospores,  it  has  been  found  that  they  range  from  7  to 
16.2  fjL  broad  by  from  16  to  36;^  long,  while  the  averages  from  different 
hosts  range  from  9.5  to  13.3  m  by  19.8  to  27.8^*.  Spores  on  the  apple 
show  a  slight  variation  on  the  different  organs,  as  follows :  on  the  fruit, 
10.6  by  25 /x;  on  the  twigs,  11. 6  by  23.8 /u;  on  large  limbs,  12.9  by  24.9/1; 
on  the  foliage,  12.3  by  23.5/x.  Paddock  (1899b:  195,  table  i)  notes 
considerable  variability  with  respect  to  size  as  the  spores  occur  on 
different  plants,  but  he  says:  "Yet  the  spores  produced  on  apple  fruits 
inoculated  with  cultures  from  either  host,  are  of  the  same  size  and 
character;  similarly,  though  not  shown  in  the  table,  when  pear  trees  are 
inoculated  with  cultures  of  Sphaeropsis  taken  from  apple  trees  the  result- 
ing pycnidia  and  spores  are  of  the  average  size  of  those  found  in  nature 
on  pear  tree  bark." 

The  mature  pycnospores  are  brownish,  varying  from  a  very  light  to  a 
dark  ferruginous  color.  The  color  darkens  with  age,  so  that  the  very 
youngest  mature  spores  are  hyaline.     The  question  of  the  maturity  of 


72  Bulletin  379 

these  colorless  spores  has  frequently  arisen.  The  writer  has  germinated 
them,  and  is  of  the  opinion  that  they  should  be  regarded  as  physiologically 
mature.  The  hyaline  color  is  replaced  later  by  a  yellowish  green  tinge, 
and  finally  a  brown  of  varying  density  is  assumed,  the  spore  becoming 
very  dark  brown  in  the  final  condition  of  coloration,  as  noted  above. 


00^:1^     0^0     9^<?0    ^J 

Fig.    25.        VARIATIONS  AND   TYPES  OF  PYCNOSPORES  OF  PHYSALOSPORA  CYDONIAE    FROM 
VARIOUS   HOSTS 

A,  Typical  unicellular  pycnospores;  B,  typical  bicellular  pycnospores;  C,  three-  and  four-celled  pycno- 
spores,  not  common;  D,  pycnospores  from  apple  twig-  E,  pycnospores  from  apple  limb;  F,  pycnospores 
from  a  single  pycnidium,  from  apple  twig;  G,  very  old  pycnospores  which  have  burst;  H,  pycnospores 
from  apple  fruit;  I,  pycnospores  from  sumac;  J,  pycnospores  from  sumac  showing  peculiar  fusion;  K, 
pycnospores  from  sumac;  L,  pycnospores  from  crab;  M,  pycnospores  from  mulberry;  N,  pycnospores  from 
rose  fruits;  O,  pycnospores  from  bittersweet;  P,  pycnospores  from  rose  of  sharon;  Q,  pycnospores  from 
witch-hazel;  R,  pycnospores  from  spicebush 

The  several  shades  of  color  may  be  represented  by  the  spores  of  a  single 
pycnidium,  although  the  majority  are  uniform  in  this  respect. 

The  typical  pycnospore  is  ellipsoidal,  frequently  tapering  slightly 
toward  the  basal  end  (Fig.  25,  a).  The  shape  also  is  a  variable  character, 
however.  Pyriform  spores  may  accompany  ellipsoidal,  globose,  or  some- 
what elongated  forms. 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits      73 

The  question  of  septation  of  pycnospores  is  of  importance  because  of 
the  fact  that  it  involves  the  systematic  value  of  the  character,  or  varia- 
tion if  it  be  so  called,  in  separating  the  form-genera  Sphaeropsis  and 
Diplodia,  and  because  of  the  physiological  significance  of  its  formation. 
In  nature,  three  possible  conditions  exist  with  respect  to  the  presence 
of  one-  and  two-celled  spores.  A  pycnidium  may  contain  only  one-celled 
spores  (Fig.  25,  a)  or  only  two-celled  forms  (Fig.  25,  b),  or  both  kinds  may 
be  present  (Fig.  2  5 ,  e  ,  p ,  Q ,  r)  .  Occasionally  three-celled  and  even  four-celled 
pycnospores  have  been  observed  (Fig.  25,  c).  It  is  a  striking  feature  in 
this  regard  that  no  strain  has  come  under  the  writer's  observation  that  will 
not  produce  two-celled  spores.  Just  what  factors  induce  cross-wall  for- 
mation is  a  matter  not  well  understood.  Mature  unicellular  spores  placed 
to  germinate,  whether  germinating  at  once  or  not,  will  sometimes  develop 
a  septiim.  Again,  spores  that  are  found  scattered  about  on  the  bark  of  the 
host  plant  show  the  bicellular  condition.  In  very  dark  spores  the  cross- 
wall  is  not  always  readily  visible  and  may  be  easily  overlooked. 

The  writer  made  observations  on  several  strains  regarding  this  character. 
Spores  were  placed  in  a  drop  of  water  and  set  in  a  moist  chamber  for  several 
hours.  At  the  beginning  and  at  the  end  of  each  experiment  the  spores 
were  examined  for  septation.  The  strains  when  collected,  with  the 
exception  of  one  (no.  64)*  on  mulberry  (Morus  alba  L.),  possessed  one-celled 
spores  only.  After  being  placed  to  germinate,  or  in  nature  after  they  had 
oozed  forth  on  the  substratum,  septa  began  to  appear  and  the  percentages 
were  as  follows:  one-celled  spores,  from  two  to  ninety-five  per  cent; 
two-celled  spores,  from  five  to  ninety-eight  per  cent;  three-  and  four- 
celled  forms,  rare.  The  average  for  all  such"  observations  shows  that  the 
percentage  of  one-  and  two-celled  forms  is  about  equal. 

Cultural  studies  were  made  of  an  apple  strain  (no.  82)  with  reference 
to  this  and  other  morphological  characters.  A  single  ellipsoidal,  brown, 
one-celled  pycnospore,  10.8  by  21  m  in  size,  from  a  pycnidixmi  in  which 
all  the  spores  were  one-celled  and  typically  like  the  one  described,  was 
isolated  on  March  3,  1913,  and  a  pure  culture  was  developed  from  it. 
Examination  of  the  culture  at  intervals  showed  the  development  of 
hyaline,  Macrophoma-like  spores.  At  the  end  of  twenty-four  days  these 
had  become  brownish,  and,  while  the  majority  were  ellipsoidal,  averaging 
from  9toiOMby2it0  22ju,  a  few  were  pyriform  and  measured  12.6  by 
30.6  iu.  At  the  end  of  fifty  days  an  occasional  spore  was  found  with  a 
cross- wall;  after  eighty  days  thirty  per  cent  of  the  spores  were  two-celled, 
and  on  May  27  sixty  per  cent  were  bicellular. 

From  the  same  culture  a  second  generation  was  originated  by  culturing 
a  one-celled,  ellipsoidal,  brown  spore,  11  by  22 /x  in  size.     The  following 

<  The  specimens  were  numbered  consecutively  regardless  of  source,  host,  and  other  considerations. 


74  Bulletin  379 

notes  were  taken:  Within  two  weeks  an  occasional  spore  measured  7.5 
by  21  M,  although  the  usual  size  was  from  9  to  10.8  m  by  19.8  to  26.1  m- 
After  forty  days  several  two-celled  spores  appeared.  At  the  end  of  two 
months,  fifty  per  cent  of  the  spores  were  one-septate. 

A  third  generation  was  initiated  by  planting  a  spore  from  the  second 
generation,  of  the  same  shape  and  measurement  as  the  preceding.  After 
one  month  twenty-five  per  cent  of  the  pycnospores  were  of  the  Diplodia 
type. 

Another  series  was  studied,  using  a  two-celled  spore  from  a  pycnidium 
in  which  both  one-celled  and  two-celled  forms  were  present.  Within  one 
generation  a  single  spore,  10.8  by  21^1  in  size,  two-celled,  brown,  ellip- 
soidal, had  developed  ofi'spring  showing  the  usual  color  variations  —  that 
is,  from  hyaline  to  greenish,  and  finally  brownish.  After  eighteen  days 
some  of  the  spores  measured  12  by  2S  n,  the  average  being  10.5  by  21  /x. 
Septation  began  to  show  after  five  weeks,  and  within  eighty  days  sixty 
per  cent  of  the  spores  examined  were  two-celled. 

Apparently,  from  a  single  pycnidium  in  which  the  spores  are  of  a  given 
type  there  may  develop  in  succeeding  generations  a  wide  variation  in  size, 
color,  shape,  and  septation.  In  an  early  stage  the  Macrophoma  type  may 
appear  in  both  size  and  color;  later  the  Eu-Sphaeropsis  type,  one-celled, 
brown;  and  finally  the  Diplodia  forms.  The  variable  shapes  that  may  be 
found  in  the  generations  succeeding  a  given  type  indicate  that  two-celled 
forms  may  be  mere  deviations  in  the  life  cycle.  On  the  other  hand.  Brooks 
and  DeMeritt  (1912:184)  report  from  New  Hampshire  a  large-spored 
form  which  holds  true  to  its  morphological  characteristics  for  several 
generations. 

Markings  on  the  wall  of  the  pycnospores  are  reported  by  Griffon 
and  Maublanc  (1910:312).  These  authors  claim  to  have  discovered  an 
undescribed  character  of  the  spores  of  this  species,  namely,  a  shagreened 
wall.  This  character  is  not  reported  elsewhere  in  literature,  and  has  not 
been  observed  by  the  writer  among  the  several  strains  studied,  including 
Dr.  Peck's  type  specimens  of  Sphaeropsis  Malorum  Peck.^ 

Long,  slender  bodies,  measuring  about  i-S/jl  in  diameter  and  often 
50/i  in  length,  have  been  observed  interspersed  between  the  pycnospores 
of  a  strain  from  apple  twigs.  They  are  not  of  frequent  occurrence  in  the 
experience  of  the  writer. 

MYCELIUM.  The  mycelium  is  composed  of  septate  tubes,  monopodially 
branched  and  comparatively  broad  — •  being  on  an  average  about  4  to 
7  M  in  diameter.  In  the  young  hyphae  cross-walls  are  rare,  but  in  older 
branches  the  threads  are  often  short  and  frequently  with  bulging  lateral 

5  Following  the  Vienna  Code  published  in  1906  (Wettstein,  R,  von,  Wiesner,  J.,  and  Zahlbruckner,  A., 
Verhandlungen  des  Internationalen  Botanischen  Kongresses  in  Wien,  1905,  p.  200),  this  specific  name  should 
be  capitalized. 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits      75 


-*=^ 


walls.  Color  is  lacking  in  young  aerial  threads,  but  as  age  increases  a 
greenish  yellow,  then  bluish  green,  brown,  and  finally  dark  brown,  hue  is 
assumed.  In  mass  the  myceliiim  ap- 
pears black.  In  cultures  lacking  potas- 
sium a  violet  tinge  has  been  observed. 
The  walls  of  the  hyphse  are  relatively 
thick,  and  sometimes  a  decided  double 
contour  of  the  membrane  is  visible. 
The    appearance   of  the  cell  contents 


Fig.   26.      PART   OF    CROSS    SECTION 
OF   SCLEROTIUM 

-varies,  apparently  depending 
somewhat  on  age  and  nutri- 
tion. Young  and  well-nourished 
cells  are  densely  granular,  while 
older  threads  contain  vacuoles 
and  glycogen  drops  in  abun- 
dance. 

SCLEROTIA  (Plate  xiii,  3, 
and  Fig.  26).  Sclerotial  bodies 
have  been  found  in  nutrient 
media  of  high  sugar  content 
and  in  oat  agar  cultures  of 
ascospores  from  Hamamelis 
virginiana.  Walker  (1908:38) 
reports  the  development  of 
sclerotium-like  bodies  resem- 
bling pycnidia  on  artificial 
media.  They  have  also  been  ob- 
served by  Baccarini  (1890:67) 
just  under  the  skin  of  the 
apple. 

CHLAMYDOSPORES    (Fig.    27).      Chlamydosporcs  have  doubtfully  been 
observed  by  the  writer  in  host  tissues.     In  a  few  cases  a  suggestion  of 


Fig.  27 


CHLAMYDOSPORES    OF    PHYS.\LOSPORA 
CYDONIAE 

Types  of  chlamydospores  found  in  pure  cultures 


76  Bulletin  379 

such  a  body  was  found  in  apple  bark.  In  old  cultures  on  various  artificial 
media,  large,  thick-walled,  intercalary,  brown,  spore-like  bodies  are  some- 
times present  in  abundance.  They  were  also  obtained  easily  by  transferring 
bits  of  myceliiim  to  sterile  water.  They  have  been  observed  in  agar  cul- 
tures that  have  become  contaminated  by  bacteria,  being  found  more 
especially  near  the  bacterial  colonies.  The  most  striking  forms  observed 
were  on  old  agar  cultures  of  the  strain  (no.  6)  from  Rhus  typhina  L. 
Similar  bodies  are  described  and  figured  by  Hedges  and  Tenny  (191 2  :  16) 
in  their  studies  on  Sphaeropsis  tumejaciens.  These  large  bodies  suggest 
young  pycnidia,  owing  to  the  form  and  cellular  structure.  All  gradations 
from  thick-walled,  colorless,  greenish  or  brownish,  granular,  swollen  cells, 
occurring  singly  or  in  chains,  are  very  common  in  artificial  culture. 
These  bodies  have  been  germinated  by  the  writer,  the  germ  tubes  de- 
veloping into  hyphas  of  the  usual  type  (Fig.  27,  near  top). 

MiCROCONiDiA(Fig.  28).     Microconidia,  or  secondary  bud-like  bodies, 
have  been  observed  in  culture  after  forty-eight  hours.     They  develop 
as  swellings  near  the  tips  of  the  growing  hyphac.     They 
are  globose  or  somewhat  pyriform,  measuring  from  3.6 
to  6.3  M  .by  7  to  14.5  n,  averaging  4  by  9.5  m- 

YEAST   FORMS.     Alwood   (1898  b)    records    the    dis- 
covery of    a  yeast   form   occurring  in  the  laboratory 
cultures  of    the    fungus,  which  on  isolation   and  rein- 
oculation  of  apple  fruit  produced  its  fruiting   bodies. 
Such  forms  have  never  occurred  in  any  of  the  writer's 
pure  cultures. 
MicRoco-       The  variations  exhibited  by  this  fungus  do  not  repre- 
LospoRACYDONiAE  ^^^^  uuique  phenomena  among  the  fungi.     Shear  and 
Showing  microconidia  Wood   (1913:63)    Say   of  Glomcrella:   "No  character, 
threadr  The  ^6^1^!-  either  morphological  or  physiological,  seems  to  be  well 

croconidia  in  the  center     r-        in        /t»-u  £J/  /:  j:  r  \        •  1 

are  magnified  800  diam-  hxcd.  i  hey  find  (page  64  ot  samc  reference)  wide 
variability  in  the  manner  of  conidial  production ;  all 
intergradations  between  a  hyphomycetous  type  and  a  distinct  melan- 
coniaceous  type  of  structure  occur  in  cultures.  Seta)  may  be  present  in 
some  cultures  and  absent  in  others,  while  paraphyses  are  regarded  as  of 
little  taxonomic  value.  Duggar  (1909 :  303) ,  in  speaking  of  the  Altemaria- 
Macrosporiiim  question,  says:  "  The  catenulate  method  of  spore  produc- 
tion has  been  reported  only  in  artificial  cultures  in  this  case,  and  it  is 
possible,  furthermore,  to  obtain  for  various  fungi  in  such  cultures  in 
general  many  variations  from  what  would  be  considered  the  normal  type 
of  spore  production  upon  the  host."  It  is  stated  in  the  same  place  that 
cultures  of  such  forms  as  Fusarium,  Gloeosporium,  and  Cercospora  yield 
variable  characters  in  culture.     Seaver  (1908)  points  out  the  misleading 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits       77 

and  misused  color  characters  in  some  of  the  Hypocreales.  Stevens  and 
Hall  (1909  b)  report  considerable  variation  in  certain  forms  under  different 
environmental  influences. 

PHYSIOLOGY 

METHODS  OF  ISOLATION.  The  chicf  mcthods  used  in  isolating  the 
organism  were:  the  plating  of  spores  in  agar  and  the  transfer  of  single 
germinating  spores ;  transfer  of  single  spores  by  the  capillary  tube  method 
as  described  previously  by  the  writer  (1913:291-292);  planting  bits 
of  diseased  tissue  in  agar  plates.  The  first  two  methods  are  advanta- 
geous in  getting  pure  lines  or  races.  The  third  method  has  practical 
advantages  in  its  simplicity  and  the  ease  with  which  the  culture  is  obtained. 

CULTURAL  CHARACTERS  —  GENERAL.  The  ability  of  this  fungus  to 
grow  on  the  commonly  used  culture  media  is  a  noticeable  physiological 
character.  It  is  easily  isolated,  and  its  appearance  in  successive  stages 
of  development  is  generally  the  same  in  all  the  culture  media  employed. 
The  colonies  are  at  first  cottony;  after  from  two  to  five  days  the  sub- 
merged threads  are  green  or  blue-green  for  about  a  week,  after  which 
the  growth  is  dark  or  nearly  black,  but  almost  without  exception  the 
outer  ends  of  the  aerial  threads  maintain  their  original  cottony  appear- 
ance. After  from  seven  to  ten  days  pycnidia  appear.  The  writer  has 
always  been  able  to  develop  pycnidia  in  culture,  although  Brooks  and 
DeMeritt  (1912:183)  found  considerable  difficulty  in  getting  cultures  to 
sporulate.  Often  a  distinct  concentric  zonation  occurs  in  plate  and  tube 
cultures.  The  exudation  in  culture  of  drops  of  liquid  has  been  observed 
frequently.  This  is  described  by  Potebnia  (1907),  who  regards  it  as  an 
excretion  product. 

The  general  characters  described  above  —  except  zonation,  which  is 
irregular  in  its  occurrence — ^  apply  to  the  following  media:  several  dif- 
ferent agars,  including  potato,  prune,  apple,  oat,  bean,  and  nutrient;  solid 
vegetable  substances,  such  as  potato  cyHnders,  bean  pods,  apple  twigs, 
and  apple  fruit  cylinders;  synthetic  liquid  media,  such  as  Fraenkel  and 
Voge's,  Cohn's,  Rankin's,  and  Uschinsky's  solutions. 

CULTURAL  CHARACTERS  —  SPECIAL.  The  writer  (1913:292-293)  has 
previously  reported  differences  in  the  growth  of  cultures  from  ascospores 
and  pycnospores  when  planted  in  -f  lo  nutrient  agar.  On  the  one  hand 
pycnospores  were  developed  within  about  one  week  from  pycnospore 
plantings,  whereas  on  the  other  hand  no  fruiting  bodies  had  appeared 
after  several  weeks  in  cultures  from  ascospores,  the  growth  remaining 
stunted.  Cultures  of  ascospores  and  of  pycnospores  were  similar  on  other 
media  (Plate  xiii,  i). 

PROTOPLASMIC  STREAMING.  Protoplasmic  Streaming  in  the  hyph.se 
has  been  studied  by  Potebnia  (1907).     He  has  found  that  movement 


78  Bulletin  379 

begins  with  the  germination  of  the  pycnospore.  The  direction  is  first 
toward  the  tip,  some  granules  moving  more  rapidly  than  others.  On 
reaching  the  tip,  those  that  have  moved  the  faster  direct  their  movement 
backward,  in  some  cases  forming  groups.  The  streaming  is  not  dependent 
either  on  evaporation  through  aerial  parts  or  on  the  structure  of  the 
protoplasm,  but  is  conditioned  only  by  apical  growth  of  the  hyphse  and 
by  inner  processes.  The  slow  movement  is  pulsative,  and  it  is  observed 
that  increased  temperature  accelerates  forward  movement  and  cooling 
often  induces  backward  flow.  It  is  suggested  that  the  streaming  is  similar 
to  the  slow  movement  observed  by  Van  Tieghem  in  the  hyphse  of  the 
Mucorales. 

PATHOGENICITY 

The  ability  of  the  organism  to  produce  the  disease,  particularly/  the 
leaf  spot  and  canker  forms,  has  been  a  matter  of  no  little  consideration. 
The  difficulties  that  are  met  in  attempting  to  infect  various  plants  have 
brought  out,  not  only  some  conflicting  results,  but  also,  what  is  more 
encouraging,  some  interesting  problems  with  reference  to  the  causal 
agent  and  the  taxonomic  relationship  of  the  so-called  species  on  the 
different  host  plants.  The  cross-infection  of  the  several  hosts,  and  the 
role  of  organisms  associated  with  Physalospora  Cydoniae  in  the  production 
of  the  lesions,  are  points  that  have  a  practical  and  scientific  bearing  on 
the  whole  problem.  The  different  foi-ms  of  the  disease  are  followed 
in  the  succeeding  discussion. 

BLACK  ROT  OF  APPLE.  The  ability  of  the  fungus  to  cause  decay  of 
ruits  was  estabHshed,  after  a  fashion,  in  1878  by  Peck,  who  writes 
1879:20)  that  "the  disease  is  contagious,  and  may  be  communicated 
rom  one  apple  to  another." 

Von  Thiimen  (1879)  ^  regards  the  fungus,  which  he  called  Diplodia 
Malorum  Fckl.,  as  a  saprophyte  rather  than  a  parasite,  but  believes  that 
it  is  capable  of  attacking  sound  finiit  and  is  able  to  cause  notable  injury 
in  storage. 

Arthur  (1885)  inoculated  sound  quinces  by  inserting  beneath  the  skin 
a  bit  of  diseased  fruit  tissue  containing  spores  of  the  fungus  (which  he 
calls  Spkaeropsis  Cydoniae  C.  &  E.).  The  inoculated  fruits  were  placed 
under  a  bell  jar.  Arthur  says:  "  The  spores  germinated,  and  the  rotting 
progressed  slowly,  when,  on  the  twenty-second  day,  the  spot  had  reached 
an  inch  and  a  half  in  diameter,  and  the  fruiting  points  had  begun  to  appear." 

Halsted  (1892)  states  that  the  fungus  grows  interchangeably  on  apple, 
quince,  and  pear  fruits.  He  reports  having  corroborated  his  laboratory 
experiments  by  field  observations. 


'  Original  not  seen  by  the  writer;  context  taken  from  Baccarini  (1890  :  70). 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits      79 

Sturgis  (1894)  made  inoculations  both  in  the  field  and  in  the  laboratory, 
confirming  the  work  of  Halsted  (1892)  and  showing  that  when  the  skin, 
was  not  broken  previous  to  inoculation  the  fruits  remained  in  a  sound 
condition. 

Paddock  (1899  b:  185)  produced  black  rot  of  apple  artificially  within 
a  few  hours  by  the  use  of  the  black-spored  fungus,  pycnidia  appearing 
after  sixteen  days.  Again,  Paddock  states  (page  193  of  same  reference) 
that  the  fungus  from  pear,  quince,  and  Japanese  plum  produces  rot  in 
apple,  pear,  and  quince,  if  the  skin  is  punctured  and  moisture  is  furnished. 

More  recent  inoculation  experiments  are  reported  by  Walker  (1908), 
Morse  (1909),  Arnaud  (191 2),  and  others. 

Two  forms  of  Sphaeropsis  were  observed  by  Walker  (1908),  both  of 
which  were  capable  of  producing  black  rot  —  the  newer  form,  however, 
being  a  more  vigorous  rot  producer.  The  morphological  differences 
have  been  previously  noted. 

The  writer  made  several  inoculations  (tables  i  and  2)  on  apples  of 
different  varieties,  using  different  strains  from  bark  and  fruit.  In  all 
cases  pure  cultures  of  the  fungus  were  used.  In  making  wounds  to  serve 
as  infection  courts  a  flamed  scalpel  was  employed.  Material  transferred 
from  the  culture  consisted  of  mycelium  and  spores;  this  was  inserted 
in  the  injury  previously  made,  and  the  fruits  were  placed  in  sterile  moist 
chambers.  It  is  to  be  noted  from  table  i  that  different  strains  vary  in 
their  ability  to  infect  the  same  variety.  Attention  is  called  to  a  comparison 
of  strains  i,  2,  3,  and  4.  All  were  used  on  Baldwin  apples  on  the  same 
date  and  under  similar  conditions,  yet  the  results  were  different.  Strains 
I  and  3  showed  slow  decay,  with  no  pycnidia  after  nineteen  days.  On  the 
other  hand,  strains  2  and  4  caused  rapid  decay  and  abundant  pycnidia 
in  the  same  length  of  time. 

As  shown  in  table  i,  nine  different  varieties  were  inoculated  with  the 
same  culture,  the  results  being  variable  with  reference  to  decay,  fruit 
body  production,  and  the  formation  of  concentric  rings. 

It  has  been  commonly  observed  that  older  cultures  produce  the  disease 
less  readily  than  do  younger  cultures.  The  best  results  were  obtained 
by  the  use  of  cultures  not  more  than  two  months  old. 

LEAF  spot  of  APPLE.  Various  theories  have  been  advanced  to  explain 
the  cause  of  the  leaf  spot  disease.  In  1902  Stewart  and  Eustace  (1902  :  228) 
believed  spray  injury  to  be  the  responsible  agency.  They  further  suggest 
(page  232  of  same  reference)  that  drops  of  rain  act  as  lenses  and  so  con- 
centrate the  rays  of  the  sun,  overheating  the  tissues  beneath.  The  belief 
is  ultimately  expressed  by  them  that  the  large  proportion  of  leaf  spot 
in  New  York  is  due  to  spray  injury  and  is  not  of  fungous  origin.  Frost 
has  been  considered  the  causal  factor  by  Stone  and  Smith   (1903)  in 


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Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits      83 

Massachusetts.  They  write:  "No  organism  was  to  be  found  as  the  cause 
of  the  injury,  and  from  the  sequence  of  events  there  could  be  no  reasonable 
doubt  that  the  frost  was  the  destructive  agency." 

The  fungus  theory  was  probably  first  favored  by  Alwood  (1892:59), 
who  attributed  brown  spot  to  Phyllosticta  pirina.  This  organism  has 
been  regarded  as  the  causal  agent  by  several  other  writers  —  Kinney 
(1895  b),  Lamson  (1899),  and  others.  In  1895  Stewart  (1896)  found  a 
new  species  of  Phyllosticta,  described  as  Phyllosticta  limitata,  responsible 
for  an  epiphytotic  of  leaf  spot  on  Long  Island.  In  1907  the  fungus 
Phyllosticta  pirina  Sacc.  was  transferred  to  the  genus  Coniothyrium  by 
Sheldon  (1907),  and  the  organism  is  now  designated  as  Coniothyrium 
pirina  (Sacc.)  Sheldon.  Another  species  of  Phyllosticta,  P.  prunicola 
Sacc,  is  listed  by  Tubeuf  and  Smith ''  as  the  cause  of  spotting  of  leaves  of 
apple,  plum,  cherry,  and  apricot. 

Alwood  (1898  a)  records,  in  addition  to  P.  pirina,  other  fungi  associated 
with  the  leaf  spot,  including  Hendersonia  Mali  and  Sphaeropsis  Malorum. 
This  is  the  earliest  record  that  the  writer  has  seen  of  the  occurrence  of 
the  last-named  fungus  on  leaves  of  apple,  although  Clinton  (1902,  and 
1904:298)  reports  it  as  the  common  cause  of  leaf  spot  in  Illinois  and 
Connecticut  in  later  years.  The  question  of  its  relationship  to  the  leaf 
spot  disease,  as  well  as  that  of  other  fungi,  was  subsequently  studied 
by  various  pathologists. 

Scott  and  Quaintance  (1907)  state  that  several  different  fungi,  most 
prominent  among  which  are  Phyllosticta  sp.,  Hendersonia  sp.,  and 
Sphaeropsis  Malorum,  are  connected  with  spots  and  may  be  responsible 
for  the  injury  in  some  ca^es,  yet  they  are  not  clear  as  to  which  are  the 
real  parasites.  The  following  year  the  subject  was  investigated  by  Hartley, 
I.  M.  Lewis,  and  Scott  and  Rorer.  Hartley  (1908  b),  in  examining  leaf 
spots  of  apple  from  the  West  Virginia  Agricultural  Experiment  Station, 
found  the  following  fungi:  Coryneum  foliicolum,  Coniothyrium  pirina,  an 
undetermined  species  of  the  Tuberculariae,  Sphaeropsis  Malorum,  Mono- 
chaetia  Mali,  Pestalozzia  breviseta,  Phyllosticta  limitata,  Torula  (?)  sp., 
Macrosporium  sp.,  Ascochyta  sp.,  Phyllosticta  (?)  piriseda  (?),  Phoma  Mali, 
Septoria  piricola  (?),  Metasphaeria  sp.,  and  an  undetermined  species  of 
Leptostromaceae.  He  expresses  the  opinion  that  probably  Coryneum 
foliicolum  was  formerly  reported  as  a  Hendersonia.  The  fact  that  the 
parasitism  of  Coniothyrium  pirina  was  questioned  by  Stewart  and  Eustace 
(1902:228)  led  Hartley  to  investigate  the  pathogenicity  of  this  species. 
He  found  that  it  would  not  affect  healthy  tissue,  but  that  on  the  other 
hand,  when  wounds  such  as  scalding,  abrasion  of  epidermis,  or  punctures 


7  Tubeuf,  K.  F.  von,  and  Smith,  W.  G.    Diseases  of  plants  induced  by  cryptogamic  parasites,  page  463- 
1897- 


84  Bulletin  379 

with  hot  and  cold  needles,  were  made  in  the  tissue,  the  fungus  in  most 
cases  grew  and  fruited.  He  concludes  that  C.  pirina  is  a  facultative,  or 
wound,  parasite  only,  and  further  that  its  ability  to  cause  leaf  spot  in 
orchard  trees  to  any  extent  remains  to  be  demonstrated.  In  his  opinion 
Coryneum  foUicolum  is  less  parasitic  in  the  field  than  Coniothyrium 
pirina. 

I.  M.  Lewis  (1908 :  367)  writes  as  follows  regarding  the  leaf  spot  situation 
in  New  Hampshire:  "Believing  that  the  exact  relation  of  all  the  fungi 
associated  with  the  spots  had  not  been  thoroughly  tested,  an  investiga- 
tion was  begun  during  the  past  summer  to  determine,  if  possible,  the 
cause  of  the  disease  as  it  occurs  in  this  State,  and  means  of  control  by 
various  spray  mixtures."  He  states  further  (page  368  of  same  reference) 
that  on  isolation  it  was  found  that  the  fungi  predominating  were  Conio- 
thyrium pirina,  Coryneum  foUicolum,  Sphaeropsis  Malorum,  Alter naria  sp., 
and  one  of  the  Tuberculariae.  To  Hartley's  total  list  of  fungi  associated 
with  apple  leaf  spots,  C.  E.  Lewis  (1912:51)  adds  Cladosporium  herbarum 
(Pers.)  Link  and  Dematium  pullulans  De  Bary,  while  Brooks  and  DeMeritt 
(191 2  :  182)  report  the  isolation  of  a  Fusariimi.  The  first  series  of  experi- 
ments made  by  L  M.  Lewis  (1908),  on  August  i  showed  that  many  inocula- 
tions did  not  result  in  infections;  from  this  Lewis  reasons  that  "the 
period  at  which  the  leaf  is  naturally  infected  is  earlier  in  the  spring  and 
summer."  This  view  is  upheld  by  C.  E.  Lewis  (1912:55),  who  concludes 
that  the  older  leaves  are  not  so  susceptible  to  infection  as  are  young 
leaves;  the  work  of  Brooks  and  DeMeritt  (1912:190).  however,  in  which 
they  conclude  that  infection  may  occur  until  the  last  of  August,  indicates 
that  the  question  of  biologic  races  was  a  factor  overlooked  by  both 
L  M.  Lewis  and  C.  E.  Lewis.  As  regards  the  general  conclusions  of 
L  M.  Lewis's  work  it  may  be  further  quoted  (1908): 

As  a  result  of  this  season's  inoculation  experiments  it  is  impossible  to  offer  more  than 
negative  results  as  to  the  cause  of  the  spots.  I  am  of  the  opinion,  however,  that  the 
fungus  Sphaeropsis  malorum  which  is  known  to  cause  canker  of  apple  limbs  and  is  an 
active  parasite,  will  be  found  to  be  the  primary  cause  of  apple  leaf  spot.  This  sup- 
position must,  however,  be  supported  by  direct  experiment  before  it  can  be  definitely 
afhrmed  for  the  spots  considered  in  this  investigation. 

The  same  year  the  results  of  further  investigations  by  Scott  and  Rorer 
(1908)  were  published,  in  which  a  definite  conclusion  was  reached.  They 
state  (page  49  of  reference  cited):  "  It  was  found  that  Sphaeropsis  mal- 
orum, contrary  to  the  general' belief,  is  the  cause  of  the  disease."  Regard- 
ing the  associated  species  they  conclude  (page  52  of  same  reference): 

Coniothyrium  pirina  (Sacc.)  Sheldon,  although  it  occurs  abundantly  on  apple  leaf- 
spots,  appears  to  have  nothing  to  do  with  their  formation. 

The  several  other  fungi  that  were  tested,  such  as  Hendersonia  sp.,  Coryneum  sp., 
Pestalozzia  sp.,  and  Alternaria  sp.,  proved  to  be  non-parasitic  in  these  experiments  and 
probably  occur  on  leaf  spots  only  as  saprophytes. 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits      85 

The  work  of  Scott  and  Rorer  is  practically  confirmed  by  C.  E.  Lewis 
(1909).  After  making  several  inoculation  experiments  the  latter  writes 
(1912:55),  in  agreement  with  Hartley  (1908  b),  as  follows: 

The  results  of  these  inoculation  experiments  seem  to  indicate  that  Sphaeropsis  is 
able  to  attack  the  leaves  of  orchard  trees  when  they  are  inoculated  early  m  the  season 
under  favorable  conditions  for  growth.  No  spottmg  has  been  produced  by  any  of  the 
other  fungi  which  have  been  tested  although  it  has  been  found  that  they  grow  readily 
on  dead  spots  which  have  been  killed  by  other  causes. 

The  investigations  of  L  M.  Lewis  began  in  1908  and  were  continued  by 
Brooks  and  DeMeritt  in  1909.  As  Brooks  and  DeMeritt  state  (1912  :  183), 
the  summer's  work  was  not  conclusive.  Later  cultural  work  revealed  to 
them  great  variation  in  the  nature  of  growth  of  different  strains  of  the 
fungus,  and  also  in  the  time  required  for  spore  production.  It  has  been 
mentioned  elsewhere  (page  68)  that  these  authors  found  morphological 
strains.  This  discovery  led  them  to  investigate  the  correlation  between 
the  morphological  and  biological  variations  of  these  forms.  Their  final  con- 
clusion (page  190  of  reference  cited)  is:  "Several  strains  of  Sphaeropsis 
Malorum  may  be  obtained,  varying  in  general  vigor  and  in  power  to  produce 
diseased  conditions.  The  large-spored  form,  with  single-loculed,  ostiolate 
pycnidia  is  largely  responsible  for  the  production  of  leaf  spot." 

The  writer  performed  inoculation  experiments  in  an  attempt  to  produce 
apple  leaf  spot  during  the  summers  of  1910  to  1913  inclusive.  In  the 
experiments  of  19 10  the  leaves  of  mature  trees  were  inoculated  in  the  follow- 
ing manner:  Pycnidia  were  removed  from  pure  culture  and  the  spores 
liberated  by  crushing  the  fruiting  bodies  in  a  watch  glass  containing  water. 
The  contents  of  the  watch  glass  were  removed  to  an  atomizer  and  the 
spores  were  sprayed  on  both  surfaces  of  the  leaves.  In  some  cases  the 
leaves  were  previously  wounded  with  a  needle,  in  others  they  were  left 
uninjured.  Data  regarding  the  source  of  the  fungus,  the  variety  and  age 
of  the  tree  whose  leaves  were  inoculated,  the  date  of  inoculation,  the  number 
of  leaves  inoculated,  and  the  results,  for  19 10  to  19 13.  are  given  in  table  3. 
It  is  to  be  noted  that  no  moist  chamber  was  provided  in  any  of  the 
experiments  of  19 10.  In  191 1  a  series  of  inoculations  made  on  May  27 
resulted  in  infection  where  wounds  and  moisture  were  provided.  The 
method  of  work  here  was  the  same  as  in  1910,  except  for  the  provision  of 
a  moist  chamber.  This  consisted  of  a  lamp  chimney,  into  which  the  in- 
oculated leaves  were  inserted  and  the  ends  of  which  were  closed  with 
damp  cotton.  The  series  of  inoculations  performed  in  July,  1910,  and  in 
August,  191 1 ,  should  be  compared.  In  neither  case  was  a  moist  chamber 
used  and  the  results  were  negative.  In  the  experiments  of  19 12  and  19 13 
no  spotting  of  the  foliage  was  obtained  by  artificial  inoculations.  The 
writer  has  no  explanation  to  offer.     The   explanation  offered  by  Brooks 


86 


Bulletin  379 


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Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits      87 

and  DeMeritt  (19 12)  for  the  leaf  spot  problem  in  New  Hampshire  is 
apparently  not  applicable  under  western  New  York  conditions,  since  a 
variety  of  morphological  forms  was  used  in  the  inoculation  work.  The 
results  obtained  indicate  that  there  is  no  correlation  between  morpho- 
logical and  biological  characters  with  respect  to  pathogenicity. 

CANKER  OF  APPLE.  Waite  (1898  a)  was  the  first  to  attribute  the  canker 
to  a  fungous  parasite;  he  suggested  that  Schizophyllum  commune  Fr.  was 
the  causal  organism.  Paddock  (1899b:  183)  found  dark  spores  on  the 
cankers,  but  supposed  they  belonged  to  some  saprophytic  form.  How- 
ever, he  grew  this  organism,  as  well  as  Schizophyllum  commune,  on  artificial 
media,  and  made  pure  culture  inoculations  in  the  following  manner:  A 
small  opening  was  made  in  the  bark  by  means  of  a  sterilized  knife,  and  a 
small  quantity  of  material  from  bean  stem  cultures  was  inserted  between 
the  wood  and  the  bark.  The  incision  was  covered  with  moist  filter  paper 
and  kept  moist  for  thirty-six  hours.  All  the  inoculations  made  in  1898 
with  the  dark-spored  fungus  on  apple  trees  were  successful;  other  fungi 
failed  and  the  wounds  soon  healed.  Paddock's  conclusions  are  sum- 
marized in  the  following  words  (page  184  of  same  reference):  "These 
experiments  showed  conclusively  that  the  dark-spored  fungus  can  pene- 
trate living  apple-tree  bark  under  certain  conditions  and  produce  a 
cankered  condition  of  apple-tree  limbs  and  also  indicated  that  it  may  pro- 
duce a  diseased  condition  of  pear-tree  bark."  Again  he  says  (page  185  of 
same  reference):  "  The  result  of  over  fifty  inoculations  made  from  cul- 
tures that  were  obtained  from  cankered  apple  tree  limbs  prove  that  the 
apple-tree  canker  of  New  York  apple  orchards  is  caused  by  a  fungus  of 
the  genus  Sphaeropsis."  Over  one  thousand  inoculations  were  made  by 
him.  in  1899  (pages  200-201  of  same  reference)  and  only  a  very  few  gave 
negative  results.  He  further  asserts  that  the  fungus  causes  canker  of  the 
quince  if  the  material  from  pure  culture  is  inserted  under  the  bark, 
whereas  under  other  conditions  the  experiments  were  not  conclusive. 

Paddock's  work  was  continued  (1900)  for  the  purpose  of  confirming 
former  results  and  to  determine  if  possible  the  relationship  between  the 
species  of  Sphaeropsis  that  occur  on  various  plants.  He  obtained  cultures 
from  apple  fruit  and  apple  bark,  and  inoculated  the  apple  tree  and  other 
plants.  The  results  were  positive,  thus  further  proving  the  pathogenicity 
of  the  organism,  as  well  as  establishing  the  identity  of  the  fungus  on  fruit 
and  bark.  The  conclusions  reached  by  Paddock  are  essentially  con- 
firmed by  C.  E.  Lewis  (1909:188-189)  and  by  McCready  (1910). 

The  writer  (1913 :  293)  has  summarized  the  results  of  earlier  inoculation 

work  as  follows: 

During  the  past  summer  [19 13]  several  inoculations  have  been  made  with  cultures 
from  the  ascospores  of  the  ascomycetous  fungus.  The  apple,  pear,  quince,  crab  apple, 
and  other  plants  were  inoculated,  in  each  case  wounds  being  made  to  serve  as  infection 


88  Bulletin  379 

courts.  Three  varieties  of  apples,  namely  Twenty  Ounce,  Baldwin,  and  Chenango 
Strawberry,  were  inoculated  between  May  20  and  July  16,  1913.  Eleven  sets  of  experi- 
ments-involving about  seventy  incisions  were  made,  all  of  which  gave  positive  infections, 
the  checks  remaining  healthy. 

The  above  quotation  concerns  the  ascomycetous  ftmgus  from  apple. 
A  morphologically  similar  organism  on  Hamamelis  virginiana  did  not 
produce  infection,  as  is  seen  from  the  following  statement  (Hesler, 
1913:293):  "About  twenty-five  different  inoculations  were  made  [with 
the  ascomycete  from  H.  virginiana]  on  all  the  plants  mentioned  above 
but  no  infections  occurred." 

The  writer  has  carried  on  inoculation  experiments  during  the  past 
four  years,  both  in  the  greenhouse  and  in  the  field,  the  most  of  the  work 
being  directed  toward  the  infection  of  bark  tissues.  The  methods  employed 
have  already  been  described  (page  79).  The  results  discussed  at  this 
point  concern  only  experiments  in  which  apple  strains  of  the  fungus 
{Physalospora  Cydoniae  Arnaud  [--=  Sphaeropsis  Malorum  Berk.])  were 
used  on  apple  itself.  The  more  important  points  in  this  regard  are  shown 
in  table  4,  indicating  the  source  of  the  strain,  the  variety  and  age  of  the 
tree  inoculated,  the  conditions  under  which  inoculations  were  made,  the 
number  of  inoculations,  and  the  general  results.  The  infection  work  done 
in  the  summers  of  1910,  1911,  and  1912  was  not  conclusive,  but  with 
the  use  of  various  strains  more  satisfactory  results  were  obtained  in  the 
season  of  1913. 

It  may  be  noted  in  table  4  that  races  of  the  fungus  came  from  different 
varieties  of  apple,  isolations  being  made  from  fruit,  leaf,  and  bark.  It  was 
desired  to  determine  if  possible  whether  strains  obviously  living  under 
saprophytic  conditions,  as  those  following  winter  injury  and  fire  blight, 
were  capable  of  inducing  bark  injury,  and  to  determine  the  nature 
of  the  parasitism  of  certain  other  strains  that  appeared  to  be  parasitic. 
The  results  on  these  points  are  conflicting  and  it  seems  that  the  strains 
are  as  variable  in  their  biological  relationships  as  in  their  morphological 
characters.  A  race  may  produce  infection  on  slightly  wounded  bark 
after  it  has  been  living  under  saprophytic  conditions,  for  example,  following 
fire  blight.  Again,  those  strains  which  in  nature  appear  to  be  acting 
parasitically  may  prove  to  be  weak  parasites,  producing  infection  only 
under  certain  conditions. 

Conflicting  results  along  this  line  have  raised  the  question  of  individual 
variation  among  varieties  of  the  host  plant  as  regards  susceptibility  or 
immunity.  It  is  possible  that  individual  hosts  in  the  same  or  in  different 
orchards  may  differ  in  this  respect,  but  conclusive  data  are  not  at  hand 
with  which  to  answer  the  question. 

The  variable  results  of  inoculations  of  the  apple  with  the  apple  fungus 
indicate  that  the  production  of  infection  requires  the  proper  strain,  a 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits 


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95 


wound  in  which  to  initiate  the  relationship,  and  moisture  until  infection 
has  occurred. 

Associated  species. —  It  has  been  noted  elsewhere  that  the  fungus 
Sckizophyllum  commune  Fr.  was  suspected  as  being  the  cause  of  canker 
(Waite,  1898  a).  This  apprehension  was  undoubtedly  based  on  asso- 
ciation of  the  fruiting  body  of  the  organism  with  the  lesions,  as  it  is  common 
to  find  this  fungus  fruiting  on  old  cankered  limbs.  Paddock  (1898  a) 
cultured  this  species  and  after  inoculating  apple  limbs  concluded  that 
it  was  not  the  cause  of  the  disease. 

The  role  of  associated  species  in  the  production  of  canker  on  apple 
is  taken  up  somewhat  at  length  by  C.  E.  Lewis  (1912).  In  Maine  the 
fungi  most  frequently  found  on  dying  twigs  and  branches  of  apple  are 
Sphaeropsis  Malorum,  Myxosporium  corticolum  Edgerton,  Coryneum 
foliicolum  Fckl.,  Cytospora  sp.,  Phoma  Mali  Schulz  &  Sacc,  and  Conio- 
thyrium  pirina  (Sacc.)  Sheldon.  Those  often  developing  in  plate  cultures 
were:  Phyllosticta  limitata  Peck,  Dematium  pullulans  De  Bary,  Clado- 
sporium  herbarum  (Pers.)  Link,  Alternaria  sp.,  Macrosporium  sp.,  Fusarium 
sp.,  Epicoccum  sp.,  and  Glomerella  cingulata  (Stonem.)  Sp.  &  von  Sch. 
To  this  list  the  writer  adds  Septoria  sp.,  Cephalothecium  roseum  Cda.,  and 
Aspergillus  sp.  C.  E.  Lewis  (1912:62)  concludes  "that  Coryneirai  and 
Phoma  can  cause  considerable  injury  to  young  trees  and  branches  of 
orchard  trees.  Myxosporium  and  Cytospora  do  not  attack  healthy 
branches  but  it  seems  probable  that  they  attack  weakened  branches." 
The  writer's  results  with  the  various  associated  fungi  may  be  summarized 
by  the  statement  that  none  of  the  species  enumerated  above  made  growth 
on  apple  bark. 

cross-inoculations  and  host  relationships  (Plates  viii,  ix,  xi,  xiv). 
The  identity  of  the  various  species  of  Sphaeropsis  on  the  same  and  on 
different  plants  has  been  established  in  certain  cases.  That  the  species  on 
the  fruit  of  apple  is  the  same  as  that  on  the  bark  was  proved  by  Pad- 
dock (1899  b,  1900)  several  years  ago,  and  confirmed  by  Potebnia  (1907) 
more  recently.  A  similar  relationship  for  the  fruit  and  foliage  forms 
of  the  fungus  has  been  proved  by  Morse  (1909),  while  Scott  and  Rorer 
(1908)  have  demonstrated  the  identity  of  the  organism  on  leaves  and 
bark.  The  ability  of  these  three  forms  to  grow  interchangeably  on  the 
several  organs  of  the  apple  is  no  longer  questioned,  and  the  results  of 
previous  investigations  are  essentially  confirmed  by  the  writer  in  tables 
I,  2,  3,  and  4. 

The  pycnidial  stage  of  Physalospora  Cydoniae  Amaud  {Sphaeropsis 
Malorum  Berk.)  has  been  collected  by  various  investigators  (Paddock, 
Arnaud,  the  writer,  and  others)  on  the  following  plants:  apple  {Pyrus 
malus  L.),  apricot  (Prunus  armeniaca  L.),  alder  {Alnus  glutinosa  Gaertn.), 


96 


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Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits      97 


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g8  Bulletin  379 

ash  {Fraxmus  americana  L.),  basswood  {Tilia  americana  L.),  bittersweet 
{Celastrus  scandens  L.),  box  elder  {Acer  negundo  L.),  cherry  {Prunus 
avium  L.,  P.  pennsylvanica  L.,  P.  virginiana  L.),  cherry  laurel  {Prunus 
lauro-cerasus  L.),  crab  {Pyrus  coronaria  L.),  currant  {Ribes  sp.),  dogwood 
{Cornus  stolonifera  Michx.,  C.  sanguinea  L.),  elder  {Sambucus  cana- 
densis L.),  elm  {Ulmus  americana  L.),  fig  {Ficus  carica  L.),  grape  {Vitis  sp.), 
hawthorn  {Crataegus  oxyacantha  L.),  hop  hornbeam  {Ostrya  virginica 
[Mill.]  K.  Koch),  lilac  {Syringa  vulgaris  L.),  maple  {Acer  saccharinum  L.), 
mulberry  {Morus  alba  L.),  oak  {Quercus  alba  L.,  Q.  prinus  L.),  osage 
orange  {Madura  pomifera  [Raf.]  Schneider),  peach  {Prunus  persica 
[L.]  Stokes),  pear  {Pyrus  communis  L.),  persimmon  {Diospyros 
virginiana  L.),  pine  {Pinus  strobus  L.),  plum  {Prunus  domestica  L.,  P. 
triflora  Roxbg.),  quince  {Cydonia  vulgaris  Pers.),  rose  {Rosa  canina  L., 
Rosa  sp.),  rose  of  sharon  {Hibiscus  syriacus  L.),  spicebush  {Benzoin 
aestivale  [L.]  Nees),  sumac  {Rhus  typhina  L.,  7?.  glabra  L.),  sycamore 
{Platanus  orientalis  L.),  witch-hazel  {Hamamclis  virginiana  L.).  Where 
fresh  material  was  available  the  writer  cultured  the  fungus  from  all  these 
plants  except  three  —  dogwood,  lilac,  and  rose  of  sharon,  which  have  just 
been  collected  —  and  these  cultures  were  used  in  all  cross-inoculation 
experiments.  The  source  of  the  cultures  used,  the  plants  inoculated,  and 
the  results,  are  shown  in  table  5.  The  methods  used  were  similar  to 
those  described  in  connection  with  the  inoculation  experiments  on  apple 
fruit  (page  79).  In  some  of  the  earlier  experiments  a  moist  chamber 
was  used  consisting  of  a  petri-dish  lid,  the  inner  margin  of  which  was  lined 
with  damp  cotton.  Later  the  glass  lid  was  eliminated  and  a  cotton  cap, 
made  by  rolling  a  strip  of  cotton  about  the  finger,  was  employed.  Moisture 
was  provided  at  the  time  of  inoculation  and  was  added  daily  for  several 
(usually  from  three  to  seven)  days  subsequently. 

The  results  of  cross-inoculations  were  not  conclusive,  particularly  in 
cases  in  which  the  fungus  failed  to  develop.  Failure  to  produce  infection 
may  be  accounted  for  in  two  ways:  either  the  fungus  was  not  parasitic 
on  the  plant  inoculated,  or  conditions  favorable  for  infection  were  lacking. 
In  many  cases  further  trials  are  desirable. 

In  nature  the  fungus  rarely  shows  a  parasitic  tendency  on  wild  plants  — 
with  the  exception  of  Quercus  prinus  (see  Rankin,  1914)  —  but  it  is 
generally  found  developing  on  dead  and  fallen  twigs;  cankers  have  not 
been  observed  which  could  with  certainty  be  attributed  to  this  organism. 
On  cultivated  plants  it  commonly  shows  the  same  habits  as  it  does  on  wild 
plants,  or  it  may  develop  in  healthy  tissues,  resulting  in  the  formation 
of  a  canker.  Here,  then,  on  the  cultivated  plants  are  found  both  sapro- 
phytic and  parasitic  tendencies.  This  phenomenon  is  in  accordance  with 
the  commonly  accepted  theory  that  parasitism  originated  from  sapro- 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits      gg 

phytism.  This  is  what  is  to  be  expected;  and  the  theory  is  further  sup- 
ported by  inoculation  data  which  show  that  the  strains  from  wild  plants 
may  be  induced  to  infect  cultivated  plants.  The  reverse  process  —  that 
is,  the  infection  of  wild  plants  with  strains  from  either  cultivated  or  wild 
forms  —  has  been  almost  wholly  unsuccessful  in  the  writer's  experience. 
This  in  the  main  confirms  the  work  of  Paddock  (iSgg  b,  igoo). 

On  certain  wild  plants  there  is  found  a  saprophytic  race  which,  when 
carried  to  cultivated  forms  such  as  the  apple  or  the  pear,  acts  as  a  wound 
parasite.  On  cultivated  plants  the  fungus  follows  fire  blight  and  winter 
injury,  and  hence  is  a  saprophyte,  but  the  latter  strains  are  not  necessarily 
obligate  saprophytes  since  they  have  been  induced  to  cause  canker  by 
artificial  inoculation.  This  is  shown  by  strains  22,38,  57,  and  70  in  table  4. 
It  does  not  appear,  therefore,  that  the  fungus  can  be  segregated  easily 
into  physiological  groups,  since  varying  degrees  of  parasitism  are  exhibited 
by  a  given  race. 

From  the  experiments  described  and  tabulated  it  is  clear  that  there  is 
considerable  variation  in  the  virulence  of  races,  but  just  how  long  a  given 
parasitic  strain  will  retain  this  mode  of  life  is  a  difficult  question  to  answer. 
The  ability  of  the  organism  to  act  as  a  wound  parasite,  and  to  adapt  itself 
naturally  to  the  saprophytic  mode,  makes  it  a  serious  pest  from  the  stand- 
point of  control.  Its  ability  to  remain  saprophytic  indefinitely  until  the 
host  is  injured  in  some  way  only  increases  the  difficulty  in  alleviating  the 
disease. 

names  and  synonymy 

The  work  that  has  been  done  on  cross-inoculations  and  on  the  mor- 
phology of  Sphaeropsis  from  several  different  plants  makes  it  apparent 
that  there  is  one  large  polymorphic  species.  It  is  true  that  many  inocula- 
tions failed,  and  that  two  given  races  may  differ  widely  in  their  mor- 
phology; but  there  is  considerable  evidence  that  these  characters  are 
variable  and  are  not  important  in  taxonomic  considerations. 

The  several  forms  as  they  have  been  described  from  time  to  time  have 
been  given  a  specific  name,  usually  one  for  every  host  plant.  This  pro- 
cedure has  resulted  in  the  acctimulation  of  a  large  number  of  specific 
names  which  could  now  be  disposed  of  only  by  the  examination  of  type 
material  of  each  so-called  species.  Several  generic  names  have  become 
involved  in  the  synonymy  of  the  fungus,  due  to  the  indefinite  limitations 
and  wide  variations,  and  consequent  overlapping,  of  certain  form-genera. 
Saccardo  (1884  a)  believed  Sphaeropsis  Malonim  Berk,  to  be  a  Phoma, 
since  it  was  originally  described  by  Berkeley  (1836)  as  having  yellowish 
green  spores.  It  is  now  known  that  the  young  spores  have  this  color 
characteristically,  and  furthermore  Dr.  C.  L.  Shear,  who  has  seen  Berkeley's 


loo  Bulletin  379 

type,  has  stated  (in  conversation  with  Dr.  Donald  Reddick,  of  Cornell 
University)  that  the  organism  is  unquestionably  identical  with  Sphaerop- 
sis  Motor um  as  now  recognized.  Subsequent  to  Saccardo's  use  of  the  name 
Phoma,  this  genus  was  divided  into  Phoma  and  Macrophoma  —  the  former 
genus  containing  species  with  spores  less  than  15/x  long,  the  latter  con- 
taining species  with  spores  more  than  15/i  long.  Thus  Phoma  Malorum 
(Berk.)  Sacc.  was  renamed  by  Berlese  and  Voglino  (1886)  as  Macrophoma 
Malorum  (Berk.)  Berl.  &  Vogl. 

It  appears  that  certain  species  of  Sphaeropsis  have  been  confused  with 
those  of  Diplodia.  The  two  genera  are  separated  on  the  basis  of  one- 
celled  spores  in  the  former  and  two-celled  spores  in  the  latter.  But 
both  genera  fail  in  their  chief  distinction,  so  that  mycologists  have  been 
misled  on  this  point.  Fiickel  (1869:393)  used  the  name  Diplodia  pseudo- 
. diplodia  Fckl.  in  describing  the  fungus  on  branches  of  apple;  elsewhere 
(page  395  of  same  reference)  he  used  Diplodia  Malorum  Fckl. 

It  has  been  noted  previously  that  the  pycnidiiim  sometimes  approaches 
and  even  reaches  the  condition  characteristic  of  the  form-genus  Botryo- 
diplodia.  It  becomes  evident  that  the  names  of  certain  species  of  this 
genus  may  stand  only  as  synonyms  of  Physalospora  Cydoniae  Arnaud. 

The  origin  of  several  of  these  synonyms  has  been  discussed  in  an  earlier 
paper  by  the  writer  (19 12),  to  which  the  reader  is  referred.  At  that  time 
it  seemed  desirable  to  attempt  the  selection  of  the  name  that  should, 
according  to  the  rules  of  priority,  be  applied  to  the  pycnidial  stage. 
Recently,  however,  the  perfect  stage  of  the  fungus  has  been  found,  and  thus 
the  selection  of  a  specific  name  from  the  pycnidial  forms  is  of  minor 
importance.  The  generic  name  now  becomes  Physalospora,  and  the 
writer  has  chosen  Cydoniae  as  the  specific  name.  The  following  state- 
ments bearing  on  this  question  are  quoted  from  another  paper  by  the  writer 
(1913:295): 

The  problem  of  selecting  a  specific  name  is  somewhat  perplexing.  The  organism 
with  which  the  writer  is  dealing  strongly  resembles  P.  Cydoniae  Arnand  but  we  have 
not  seen  his  type  material  and  there  remains  the  question  of  whether  his  fungus  has  not 
been  previously  described.  In  this  connection  a  few  species  which  suggest  this  possi- 
bility may  be  noted:  P.  entaxia  E.  &  E.,  P.  fesiucae  (Lib.)  Sacc.  and  P.  nigroptinclata 
Rom  ell,  the  last  on  limbs  of  Pyrus  malus  according  to  Saccardo.  Until  further  data 
are  at  hand  the  writer  is  inclined  to  accept  tentatively  the  name  Physalospora  Cydoniae 
Arnaud. 

Soon  after  the  above-mentioned  paper  appeared  in  print,  the  writer 
received  from  Arnaud  a  glycerin-jelly  mount  of  his  type  material.  It 
is  clear  that  morphologically  the  organism  is  identical  with  the  one 
described  by  the  writer  (1913)  under  the  same  name.  But  the  question 
of  the  specific  name  is  still  unsettled,  for  it  is  not  improbable,  as  stated 
above,  that  the  organism  has  been  previously  described  under  some  other 
specific  name.     This  problem,   as  in  the  case  of  the  several  pycnidial 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits      lor 

forms,  would  involve  the  study  of  type  material,  which  as  yet  has  not 
been  available  to  the  writer.  Under  the  circumstances  Amaud's  specific 
name  will  be  retained  tentatively  by  the  writer.  The  following  is  a 
partial  list  of  species  which  are  concerned  in  the  synonymy  of  the  fungus ; 
citations  to  literature  are  also  given: 

Physalospora  Cydoniae  Arnaud.  Ecole  Nat.  d'Agr.  Montpellier. 
Ann.  12 :  7.     1912. 

Sphaeria  siimachi  Schw.     Amer.  Phil.  Soc.     Trans,  n.  s.  4:205.     1834. 
Sphaeria  rhuina  Schw.     Amer.  Phil.  Soc.     Trans,  n.  s.  4:218.     1834. 
Sphaeria  pomorum  Schw.     Amer.  Phil.  Soc.     Trans,  n.  s.  4:219.     1834. 
Sphaeria  Malortim  Berk.     Enghsh  Flora  5:257-258.     1836. 
Diplodia  pseudodiplodia  Fckl.     Symbolae  Mycologicae,  p.  393.     1869. 
Diplodia  Malorum  Fckl.     Symbolae  Mycologicae,  p.  395.     1869. 
Sphaeropsis  Cydoniae  C.  &  E.     Grevillea  6:84.     1878. 
Sphaeropsis  Malorum  Peck.     Sylloge  Fungorum  3:294.     1884. 

Several  years  ago  Ellis  (1880)  studied  the  variability  of  Botryosphaeria 
Juliginosa  (M.  &  N.)  E.  &  E.  [=  Sphaeria  Quercuum  Schw.],  and  came  to 
the  conclusion  that  this  species  really  included  at  least  eighteen  so-called 
species.  Among  these  may  be  noted,  using  Ellis's  nomenclature,  Sphaeria 
entaxia  C.  &  E.  [=  Physalospora  entaxia  Sacc],  5.  viscosa  C.  &  E.  [-=  P. 
viscosa  Sacc],  5.  erratica  C.  &  E.  [=  P.  erratica  Sacc],  Botryosphaeria 
pustulaia  Sacc,  and  others.  Ellis  found  wide  variation  with  respect  to 
stromatic  formation.  Sometimes  the  perithecia  were  scattered  and 
distinct,  and  again  they  were  confluent  and  united  in  a  stroma.  Consider- 
able range  with  respect  to  the  ostiolum  is  also  noted  by  Ellis  (1880).  But, 
as  stated  by  Ellis  and  Everhart  (1892:547),  certain  forms  of  Botryo- 
sphaeria fuiiginosa — those  lacking  a  stroma — are  removed  to  the  genus 
Physalospora.  It  may  be  that  under  certain  conditions  P.  Cydoniae 
develops  a  stroma,  but  such  a  tendency  has  not  been  observed;  for  this 
reason  the  generic  name  Physalospora  is  selected. 

LIFE  HISTORY  STUDIES 

The  mature  morphological  structures  of  the  fungus  have  been  described, 
so  that  the  following  paragraphs  concern  only  the  successive  stages  in  its 
development:  where  and  in  what  condition  the  organism  hibernates,  the 
manner  in  which  it  is  disseminated,  its  entrance  and  effects  on  the  plants 
attacked,  and  the  development  of  certain  of  its  fruiting  bodies. 

SOURCE  OF  THE  INOCULUM.  The  fuugus  passes  the  winter  as  myceliimi 
in  the  tissues  of  the  host  and  as  pycnospores  in  pycnidia.  If  a  canker 
is  examined  in  the  spring  when  growth  is  resumed  by  the  host  plant, 
the  margin  of  the  old  lesion  may  show  discoloration.  The  writer  has 
frequently  planted  bits  of  the  bark  from  the  edge  of  a  canker  in  agar 
plates,  pure  cultures  resulting.  This  is  evidence  of  the  resumption  of 
growth  of  the  mycelium  in  the  old  lesion.     It  is  stated  by  Caesar  (1909) 


I02  Bulletin  379 

that  as  a  rule  the  fungus  does  not  die  out  but  continues  to  extend  in  every 
direction  year  after  year,  finally  girdling  the  limb.  In  this  connection 
Paddock  (1899b:  189)  writes  as  follows:  "In  some  instances  the 
mycelium  apparently  lives  over  winter  and  continues  its  growth  the 
following  spring.  The  formation  of  the  largest  cankers  can  scarcely 
be  explained  in  any  other  way."  He  adds,  however,  that  "in  all  of  the 
inoculations  made  in  the  spring  of  1898,  in  only  one  instance  did  the 
resulting  canker  enlarge  any  during  the  present  season." 

The  writer's  experience  in  this  regard  is  somewhat  similar,  although 
more  cankers  have  enlarged  the  second  year  than  is  intimated  by  Paddock. 
On  this  point  there  appears  to  be  a  difference  in  orchards.  In  one  orchard 
the  author  counted  forty  cankers  on  three  trees  on  May  20,  1912.  All 
were  formed  at  least  one  year  previously,  but  only  one  showed  advance- 
ment at  the  margin  on  this  date.  In  other  orchards  a  majority  of  the 
cankers  were  enlarging.  The  vitality  of  the  trees  does  not  seem  to 
explain  the  difference  displayed,  since  this  quality  appeared  similar  in  the 
two  cases  mentioned.  The  trees  in  the  two  orchards  were  of  the  same 
variety  (Twenty  Ounce) ;  here  the  question  of  physiological  races  may 
throw  light  on  the  subject. 

It  has  been  suggested  that  the  mycelitim  may  winter  over  in  mummified 
fruit,  and  that  in  cases  in  which  the  fruit  hangs  on  the  tree  the  hyphas 
may  pass  into  the  branch  supporting  it  (Anonymous  reference,  1899  c, 
page  126).  The  latter  condition  has  not  been  observed  by  the  writer. 
In  some  cases  the  mycelium  hibernates  in  the  mummified  fruit,  but  the 
passage  of  the  hyphas  down  into  the  branch  and  the  resulting  development 
of  a  canker  is  questionable. 

The  growth  of  the  mycelium  at  the  edge  of  a  lesion,  as  described  above, 
does  not  account  for  new  and  isolated  cankers.  The  phenomenon  results 
nevertheless,  indirectly,  in  a  source  of  inoculum,  in  that  fruit  bodies  may 
develop  on  the  newly  infected  margin  and  so  furnish  spores  which  may 
cause  other  infections  directly.  The  young  cankers  originate  by  the 
agency  of  the  spores  of  the  fungus. 

It  is  a  common  thing  to  find,  in  the  winter  and  spring,  pycnidia  bearing 
mature  spores  on  mummified  fruits.  These  fruiting  bodies  may  be 
observed  also  on  cankers  and  on  fallen  twigs,  bark,  and  leaves.  In  western 
New  York  cankers  and  dead  twigs  are  the  most  important  sources  of 
the  inoculum. 

■  The  hibernation  of  pycnospores  on  the  various  organs  of  the  tree  is 
reported  by  a  number  of  investigators:  on  the  bark,  fallen  twigs,  and 
cankers,  by  Paddock  (1899  b:  189),  by  Brooks  and  DeMeritt  (1912:189), 
and  by  Scott  and  Rorer  (1908:52);  on  fallen  leaves  by  Reed  and  Cooley 
(191 1);  on  the  fruit,  as  mummies  hanging  on  the  tree  or  fallen,  by  Scott 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits     103 

and  Rorer  (1908:52)  and  by  Brooks  (1909).  Other  writers  have  con- 
firmed air  these  observations.  These  spores  in  winter  have  been  placed 
in  room  temperature,  and  were  subsequently  found  to  be  capable  of 
germination  in  tap  water.  There  is  evidence  that  pycnospores  may 
also  winter  over  scattered  about  on  the  bark;  they  have  been  found  in 
early  spring  before  the  pycnidia  have  entered  their  period  of  spore  discharge. 

The  role  of  the  ascosporic  stage  in  hibernation  is  not  certain.  As 
previously  indicated,  the  perithecia  are  rare  on  Pyrus  malus  in  New 
York,  and  it  would  seem,  therefore,  that  the  ascospores  from  this  source 
are  of  relatively  little  importance  in  initiating  infections.  Whether 
this  stage  is  common  on  other  plants  in  this  State,  and  important  as 
a  source  of  inoculum,  are  matters  remaining  to  be  investigated. 

METHOD  OF  SPORE  DISCHARGE.  The  manner  in  which  the  pycnospores 
escape  from  the  pycnidium  has  not  been  fully  described,  so  far  as  the 
, writer  knows.  Berkeley  (1836)  makes  mention  of  the  process  as  follows: 
"When  dry  the  ostiolum  is  frequently  crowned  with  a  short  minute  ten- 
dril oozing  out  from  the  perithecium."  Halsted  (1892)  writes:  "  The 
ripe  spores  ....  form  long,  slender  coils  as  they  are  pushed 
out  of  the  small  hole  in  the  skin."  Similar  descriptions  of  the  process 
are  given  by  Clinton  (1902)  and  by  Evans  (19 10). 

If  a  bit  of  bark  or  of  fruit  bearing  pycnidia  is  placed  under  moist  con- 
ditions, in  a  few  hours  dark  masses  of  spores  in  the  form  of  a  coil  may  be 
seen  (Plate  xiii,  4).  In  one  experiment  the  following  notes  were  taken: 
"Twigs  of  an  apple  strain  (no.  82)  bearing  mature  brown  pycnospores 
were  placed  in  a  moist  chamber  on  May  20,  1913,  at  3  p.  m.  By  noon 
on  May  23  the  dark  masses  could  be  seen  with  the  naked  eye.  These 
masses  measure  about  200  to  250 /x  by  400  to  450 /^."  At  this  time  it 
was  observed  that  the  masses  stood  out  from  the  surface  of  the  bark 
nearly  five  millimeters.  They  were  very  easih^  removed  by  a  needle 
and  examined  under  the  microscope.  It  was  observed  that  on  the  side 
of  the  mass  nearest  the  bark  several  spores  had  germinated,  and  the 
resulting  hyphse  had  raised  the  mass  away  from  the  surface  of  the  bark. 
A  drop  of  water  was  added  to  one  mass,  which  behaved  as  follows:^  In 
a  few  seconds  the  mass  began  to  segregate,  and  single  spores  or  groups 
of  a  few  moved  very  qtiickly,  with  a  darting  motion,  from  the  mass.  They 
were  at  first  thrown  through  the  drop  of  water  as  far  as  85  /x  and  they 
then  moved  slowly  away.  After  forty-five  minutes  the  spores  had  scattered 
in  all  directions,  from  1500  to  2800 /i  from  the  original  point  of  departure. 
The  coil  in  some  cases  contained  about  1500  mature  spores  and  in  some 
experiments  proved  to  be  at  least  one  millimeter  in  length.  It  has  been 
estimated  by  the  writer  that  there  may  be  as  many  as  150  pycnidia  on 
a  square  centimeter  of  the  surface  of  an  apple  fruit;  this  would  furnish 


I04  Bulletin  379 

approximately  225,000  spores  for  the  given  unit  area,  or  1,406,250  spores 
per  square  inch  of  apple  surface. 

As  stated  in  the  notes  quoted  above,  the  spore  coils  were  found  on  the 
bark  three  days  after  moisture  was  supplied.  But  this  does  not  mean  that 
all  this  time  was  involved  in  the  process  of  escape.  The  pycnidia  were 
found  to  be  closed  at  first  and  considerable  time  must  have  been  con- 
sumed in  their  opening.  In  other  experiments  as  long  a  period  as  five 
days  was  necessary  to  efTect  the  opening  in  some  cases.  The  time  that 
actually  intervenes  between  admission  of  moisture  to  the  spore  mass 
within  the  pycnidiimi  and  the  coiling  of  the  spores  is  negligible.  Pycnidia 
have  been  removed  from  dry  bark  in  the  summer,  placed  on  dry  slides, 
and  observed  with  the  microscope.  If  a  drop  of  water  is  then  applied, 
the  spores  will  ooze  out  immediately  provided  the  ostiole  is  open.  Their 
fate  after  coiling  seems  to  depend  on  the  amount  of  moisture  present. 
If  a  beating  rain  is  falling,  undoubtedly  the  spores  are  carried  by  the 
spattering  drops  toward  the  ground  and  perchance  lodge  on  the  foliage 
or  on  the  branches.  In  case  of  a  dew,  unquestionably  the  coil  behaves 
as  described  above;  that  is,  some  of  the  spores  on  the  lower  side  of  the 
mass  germinate,  the  resulting  weft  of  germ  tubes  raising  the  spores  from 
the  bark,  when  they  may  be  lifted  by  the  wind.  Again,  if  the  mass 
encounters  a  drop  of  water  the  gelatinous  material  quickly  expands  and  the 
spores  are  scattered  throughout  the  drop.  It  is  conceivable  that  the 
drop  may  be  carried  by  the  wind  for  a  short  distance  at  least. 

TIME  OF  SPORE  DISCHARGE.  The  time  of  the  year  when  spores  are  dis- 
seminated may  be  approximated  by  noting  the  date  of  the  first  appearance 
of  the  diseased  spots,  and  by  keeping  careful  watch  of  the  behavior  of  the 
pycnidia  in  the  field.  It  is  believed  by  I.  M.  Lewis  (1908)  that  the  period 
when  foliage  is  naturally  infected  is  early  in  the  spring  and  summer.  The 
same  opinion  is  expressed  by  Brooks  (1909),  who  states  that  the  indi- 
cations are  that  leaf  infection  ceases  in  June.  Later,  however.  Brooks 
and  DeMeritt  (191 2  :  189)  attach  little  value  to  this  statement,  expressing 
the  opinion  that  the  nature  of  the  fungus  was  a  factor  overlooked  by 
previous  investigators  and  that  weather  conditions  may  play  a  part  in 
determination  of  the  time  of  infection. 

Paddock  (1899  b:  189)  states  that  many  spores  remain  in  pycnidia  until 
the  following  spring,  when  they  are  disseminated.  Wolf  (1910')  has  made 
a  study  of  the  prevalence  of  fungus  spores  in  orchards  by  exposing  agar 
plates,  and  his  conclusions  are  expressed  as  follows  (page  202  of  reference 
cited):  "At  no  time  during  the  period  in  which  exposures  were,  made 
(September  to  May,  inclusive)  were  viable  spores  of  Sphaeropsis  malorum 
present  in  the  atmosphere  of  the  orchard."  McCready  (19 10)  reports 
mature  spores  as  being  disseminated  from  cankers  as  early  as  the  first 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits     105 

week  in  April,  and  states  that  at  the  same  time  a  large  number  of  spores 
were  found  in  the  orchard  on  rotten  apples.  In  Virginia,  at  Blacksburg, 
Reed  and  Cooley  (191 1)  found  spores  being  discharged  from  pycnidia  on 
leaves  on  June  25,  19 10.  Whether  spores  are  liberated  at  an  earlier  date 
these  authors  do  not  state,  but  it  is  probable  that  such  is  the  case. 

From  observations  made  by  the  writer  it  seems  that  the  date  of  first 
discharge  in  the  spring  varies  with  the  season.  Apparently  the  ostiole 
does  not  open  at  a  temperature  below  60°  F.  (15.5°  C.)  or  in  the  absence 
of  moisture,  and  a  period  of  humidity  of  several  hours  duration  is  neces- 
sary. The  dates  for  spore  discharge  observed  at  Byron,  New  York, 
are  May  16,  1912,  and  May  12  and  23,  1913.  In  191 1  spores  were  found 
coiling  on  July  17,  but  the  process  must  have  occurred  earlier.  That 
they  continue  to  be  liberated  throughout  the  summer  is  shown  by  the 
appearance  of  new  infections  on  foliage  from  May  until  September  20, 
1913.  In  1911  several  young  spots  were  found  on  bark  in  the  middle  of 
August.  Ripe  and  green  fruit  infections  also  show  that  spores  are  dis- 
seminated in  August  and  September. 

AGENTS  OF  DISSEMINATION.  It  is  clear  that  the  behavior  of  the 
pycnospores  on  being  discharged  places  them  at  the  disposal  of  wind,  rain, 
and  possibly  insects,  depending  largely  on  the  conditions  of  moisture. 
Halsted  (1892)  states  that  "the  germs  pass  ....  through  the  air 
or  by  means  of  the  various  insects  that  visit  the  fruits,  especially  those  with 
broken  stirfaces  due  to  partial  decay."  A  similar  opinion  is  expressed  by 
Sturgis  (1894).  Lamson  (1902  :  76)  states  that  the  spores  are  easily  floated 
in  slight  currents  of  air,  while  Bethune  (1909:29)  and  McCready  (1910) 
attribute  dissemination  to  the  wind. 

The  writer  has  observed  numerous  cases  of  the  disease  in  isolated  situa- 
tions. In  some  orchards  there  was  abundant  leaf  spot  but  no  cankers 
were  on  the  trees.  Here  the  \vihd  probably  acted  as  the  agent,  carrying 
the  spores  from  plants  outside  the  orchard.  That  the  rain  washes  the 
spores  to  the  foHage  is  shown  by  the  cone-shaped  area  of  infections  beneath 
cankers  and  diseased  fruits. 

Insects  are  no  doubt  agents  in  the  dissemination  of  the  organism.  The 
gelatinous  nature  of  the  spores  renders  them  sticky  and  they  may  adhere 
to  the  feet  of  insects.  In  June,  1913,  the  writer  found  spores  on  the  feet 
of  the  rosy  apple  aphis  (Aphis  sorhi  Kaltenbach),  but  it  is  his  opinion 
that  insects  are  of  little  importance  in  carrying  the  spores.  Their  role 
in  making  openings  in  the  fruit  and  bark  is  probably  much  more  important. 

INFECTION  COURTS.  The  fungus  shows  little  preference  for  any  par- 
ticular type  of  injury  as  a  means  of  entrance.  It  is  not  able  to  penetrate 
healthy  tissue  of  the  bark  and  fruit,  but  follows  other  fungi  such  as 
Glomerella  cingulata  (Stonem.)  S.  and  vS.  on  fruit,  as  noted  by  Alwood 


io6  Bulletin  379 

(1902:257).  Other  points  of  entrance  to  fruit,  as  listed  by  Burrill  and 
Blair. (1901),  are  insect  punctures,  mechanical  injuries,  and  the  blossom 
end  of  the  apple.  These  authors  state  also  that  the  fungus  seems  to  start 
without  the  aid  of  a  wound.  The  writer  has  noted  many  cases  in  which 
young  lesions  on  the  apple  surrounded  an  opening  made  by  the  codling 
moth  (Carpocapsa  pomonella  L.).  Delacroix  (1,903  a:  140)  is  disposed 
to  believe  that  in  some  cases  certain  insects  are  able  to  rupture  the  bark, 
especially  that  of  young  branches.  He  observed  an  abundance  of  Epidi- 
aspis  piricola  (Del  Guer.)  Cld.  on  infected  areas,  and  is  of  the  opinion  that 
these  insects 'are  concerned  here.  Giissow  (191 1)  states  that  "apples 
are  infected  through  some  injury  (wasps,  curculio,  hail,  etc.,  etc.)." 
Arnaud  (19 12)  believes  that  there  is  some  connection  between  the  entrance 
of  the  fungus,  and  a  beetle. 

Observations  show  also  that  various  mechanical  injuries  commonly 
serve  as  points  of  entrance  for  the  fungus.  Such  injuries  as  limb  and 
hail  bruises  may  act  in  this  capacity.  Faurot  (19 12)  states  that  rot 
occurs  largely  on  fruits  the  skin  of  which  was  previously  broken  by  spray 
injury  and  growth  cracks. 

Whether  the  healthy  epidermis  of  the  fruit  is  penetrated,  as  suggested 
by  Burrill  and  Blair  (1901),  is  open  to  question.  The  writer  has  never 
been  able  to  infect  unbroken  tissues  of  the  apple  fruit.  On  the  foliage, 
artificial  inoculations  by  various  investigators  —  Scott  and  Rorer  (1908), 
Brooks  and  DeMeritt  (19 12),  and  others  —  show  that  the  fungus  can 
penetrate  healthy  leaf  tissues.  The  author,  however,  has  never  been 
successful  in  producing  leaf  spot  without  first  wounding  the  tissue.  Infec- 
tions in  the  bark  apparently  occur  only  through  some  sort  of  wound. 
Such  injuries  may  be  caused  by  growth  cracks,  as  noted  by  Caesar  (1909) ; 
by  ladders  and  boots,  in  pruning  and  pickiiig;  by  barking  by  the  machinery, 
in  cultivation;  by  props  not  carefully  wrftpped;  by  hail;  by  openings  left 
by  the  careless  removal  of  water  sprouts;  and  in  other  ways.  Of  fifteen 
young  cankers  observed  by  the  writer  on  a  single  tree,  ten  had  their  origin 
in  openings  left  by  the  removal  of  suckers.  The  writer  has  observed 
cases  in  which  the  fungus  had  followed  the  rust  fungus,  Gymnosporangium 
Juniperi-virginianas  Schw.,  on  apple  twigs.  Scott  and  Rorer  (1909: 11) 
suggest  that  it  may  follow  Phyllosticta  solitaria  E.  &  E.  on  apple  buds. 
The  writer  has  frequently  isolated  the  fungus  from  lesions  caused  by 
the  blotch  fungus  (P.  solitaria)  on  apple  fruits  sent  from  Indiana.  As 
previously  noted,  the  fungus  frequently  follows  fire  blight  and  winter 
injury.  Morse  and  Lewis  (1910)  state  that  in  Maine  orchards  much  of 
the  disease  that  was  called  canker  had  its  origin  in  frost  spots  of  1906- 
1907,  and  that  so  far  as  investigated  the  cankers  of  fruit  trees  in  Maine 
orchards  had  their  origin  in  wounds. 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits     107 


PYCNOSPORE  germination  (Fig.  29).  The  pycnospores  usually  ger- 
minate readily  in  tap  or  rain  water.  The  time  required  for  the  process 
varies  considerably,  depending,  no  doubt,  on  the  age  of  the  spores.  If  they 
overwinter,  the  question  of  their  longevity  arises.  As  a  rule  sexual  spores 
are  regarded  as  short-lived,  but  it  is  not  so  in  the  case  of  this  fungus. 
Duggar  (1909:353)  says:  "The  spores  seem  to  retain  their  vitality  for  a 
considerable  period  of  time,  having  been  germinated  after  being  stored  for 
a  year  in  the  laboratory."  The  writer  has  found  that  spores  two  years  old 
or  older  may  germinate  in  tap  water  after  twenty-four  hours.  Younger 
spores  ordinarily  germinate  within  five  or  six  hours,  but  they  may  pro- 
duce a  tube  after  three  hours.  Spores  which  are  dark  brown  in  color, 
often  septate,  and  having 
an  older  appearance,  re- 
quire more  than  twelve 
hours  for  germination. 

Usually  one  or  two 
tubes  emerge  from  a 
spore  at  or  near  the  end ; 
germinations  also  occur 
at  the  side.  The  de- 
veloping hyphae  in  cul- 
ture occasionally  form 
microconidia,  or  second- 
ary conidia,  near  the 
growing  point  of  a  hypha ; 
these  have  been  men- 
tioned by  Delacroix 
(1903  a:  139),  who  states 
that  they  do  not  develop  * 

further.  The  writer  has  germinated  them  in  tap  water.  In  some  cases 
peculiar  types  of  germination  occur,  short,  stunted  tubes  being  developed. 
In  other  cases  the  process  is  entirely  inhibited,  and  in  certain  of  these 
cases  the  laying  down  of  a  cross-wall  takes  place  instead.  In  one  obser- 
vation notes  were  made  as  follows : 

Spores  one-celled  when  collected  (May  13,  1913)-  Placed  to  germinate  in  tap  water 
and  after  twenty-four  hours  the  two-celled  spores  had  not  germinated;  the  one-celled 
spores  had  developed  tubes  about  30  m  long.  After  forty- two  hours  some  of  the  two- 
celled  spores  developed  tubes  about  175/x  in  length,  whereas  the  germ  tubes  of  the 
one-celled  forms  were  about  500 1^  long. 

Again,  spores  placed  to  germinate,  instead  of  producing  a  germ  tube, 
after  several  days  developed  a  septum.  Another  peculiar  behavior  of  the 
spores  is  that  they  may  fuse  in  pairs.  Delacroix  (1903  a)  describes  a 
peculiar  type   of  germination  of  young  and  hyaline  pycnospores  in  a 


Fig.  29. 


TYPES  AND  VARIATIONS  OF  PYCNOSPORE  GERMI- 
NATION 


io8 


Bulletin  379 


solution  of  2.5  per  cent  of  glucose  and  i  per  cent  of  peptone.  No  cross- 
wall  was  developed.  After  the  third  day  the  wall  broke  and  the  contents 
emerged,  forming  a  bud  on  the  surface  of  the  spore.  This  spherule  may 
attain  a  diameter  of  from  35  to  40  ju;  its  further  development  was  not 
followed  by  Delacroix.  The  writer  has  observed  similar  behavior  of 
pycnospores,  except  that  the  swollen  parts  finally  developed  a  germ 
tube.  This  took  place  in  tap  water.  In  some  cases  older  spores  burst 
and  fail  to  send  out  a  germ  tube. 

The  effect  of  low  temperatures  on  pycnospore  germination  was  noticed 
in  the  spring  of  19 13  in  connection  with  infection  experiments.  On  May 
15,  191 2,  spores  in  drops  of  tap  water  on  a  glass  slide  were  placed  in  a  petri 
dish,  plenty  of  water  was  supplied  to  prevent  drying  out,  and  the  culture 
was  placed  out  of  doors,  where  the  temperature  ranged  between  8°  and 
10°  C.  A  second  culture  was  kept  at  room  temperature  (21°  C).  No 
germinations  occurred  outside,  but  the  cultures  kept  in  the  laboratory  at 
21°  C.  gave  normal  germinations.  On  May  12,  19 13,  the  minimum  tem- 
perature was  9°  C,  the  maximum  15.5°  C.  All  spores  out  of  doors  failed 
to  germinate  at  these  temperatures,  while  those  at  21°  C.  gave  normal 
germination.  On  May  13,  19,  and  20,  1913,  when  the  maximum  tempera- 
ture was  15.5°  C,  similar  results  were  obtained,  except  that  in  one  culture 
on  Mav  20,  at  1 5.5°  C,  a  very  low  percentage  of  germination  was  observed. 

This  indicates  that  in  most  cases  a 
temperature  of  15.5°  C.  is  unfavorable 
for  germination,  and  that  below  that 
point  germination  fails.  Delacroix 
(1903  a:  139)  states  that  mature  spores 
germinate  after  forty-eight  hours 
at  a  temperature  of  about  16°  C. 
(60.8°  F.). 

ASCOSPORE    GERMINATION    (Fig.   30). 

The  ascospores  germinate  readily  in 
tap  water  and  potato  agar.  The  time 
required  for  the  process  is  from  six  to 
twelve  hours.  In  some  cases  a  septum 
is  developed  in  the  ascospore  during 
germination. 

INCUBATION  PERIOD.  The  period  of 
incubation  on  apple  bark,  as  stated  by 
Potebnia  (1907:16),  is  about  four 
days.      On    foliage    it    is    about    five 

days,   according  to  the  observations  of  Scott  and  Rorer   (1908:50-51). 

Inoculations  made  by  the  writer  on  bark  show  that  the  time  between 


Fig.  30.     STAGES  in  the  germination 

OF  ASCOSPORES 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits     ioq 

inoculation  and  the  first  sign  of  the  disease  is  from  two  to  seven  days, 
varying  with  the  strains  of  the  fungus  used  and  the  meteorological  con- 
ditions. The  average  is  four  days.  On  fruit,  discoloration  appears  after 
from  twenty-four  to  forty-eight  hours. 

PATHOLOGICAL  HISTOLOGY.  Fruit.—  If  a  scctiou  of  an  apple  fruit  is 
made  perpendicular  to  the  surface,  the  cuticle,  epidermis,  hypodermis, 
cortex,  and  scattered  vascular  bundles  are  in  evidence.  The  epidermis 
is  composed  of  a  single  layer  of  rectangular  cells,  the  outer  walls  of 
which  are  strongly  thickened  by  a  waxy  infiltration  to  form  the  cuticle. 
Immediately  below  the  epidermal  cells  is  the  hypodermal  parenchyma, 
the  cells  of  which  are  distinctly  different  from  those  more  deeply 
seated.  They  are  compactly  arranged,  comparatively  small,  and  oblong, 
with  the  greater  diameter  parallel  to  the  surface.  They  contain  the 
coloring  matter  of  the  fruit.  There  is  a  gradual  transition  from  these 
cells  to  the  large  isodiametric  cells  that  make  up  the  mass  o£  the  apple 
tissue.  The  veinlets  come  from  ten  main  veins  and  by  continued 
branching  the  bundles  become  scattered,  being  finally  lost  in  the 
cortex. 

There  is  a  sharp  line  of  demarcation  between  the  healthy  and  the 
diseased  tissues  (Plate  xii,  2);  this  is  especially  noticeable  in  the  hypo- 
dermal  parenchyma.  The  coloring  matter  is  abundant  in  the  normal  cells 
of  the  hypodermis;  at  the  junction  of  the  two  regions  the  coloration  is  lost 
very  abruptly  and  the  tissue  is  a  distinct  brown.  All  the  affected  region 
is  brown  and  the  discoloration  in  the  cortex  extends  beyond  that  in  the 
hypodermis.  Apparently  the  hypodermis  is  attacked  along  the  advancing 
margin  of  the  lesion  from  the  cortex  below.  The  mycelium  of  the  fungus 
is  found  in  advance  of  any  apparent  change  in  the  normal  color,  and  is 
found  in  the  cortex  first,  at  a  point  several  cells  in  advance  of  the  affected 
hypodermal  cells.  The  hypodermis  appears  to  be  undermined.  The  walls 
of  the  cells  in  this  region  are  greatly  thickened;  the  process  is  apparent 
within  a  week  after  infection,  and  when  the  apple  becomes  mummified 
the  lumen  of  the  cell  is  nearly  closed.  Dandeno  (1906)  states  that  there 
is  a  production  of  cellulose  in  the  cell  wall  of  the  apple  in  the  course  of 
its  decomposition.  Starch  is  also  produced  in  the  cells  invaded  by  the 
mycelium  of  the  fungus,  but  with  the  thickening  the  starch  grains  dis- 
appear. The  excessive  thickening  is  regarded  by  Dandeno  as  resulting 
in  the  preservation  of  the  mummy. 

The  mycelium  is  usually,  if  not  always,  intercellular.  In  thick,  free- 
hand sections  strands  may  be  found  crossing  the  cell  cavity,  but  cell-wall 
penetration  has  not  been  observed.  Frequently  small  threads  appear 
to  pass  into  the  cell  of  the  host  from  the  parent  branch  which  is  in  the 
intercellular  space,  but  no  opening  in  the  host-cell  wall  has  been  seen. 


Bulletin  379 


IG. 


Such  hyphai'  are  regarded  as  being  intercellular,  merely  giving  the  appear- 
ance of  an  intracellular  habit  because  of  the  thickness  of  the  section; 

in  thin,  microtomed  sections 

the  threads  are  found  be- 
tween the  cells.  In  certain 
cases  the  hyphas  appear  to 
be  within  the  cells,  but  one 
may  mistake  a  large  intercel- 
lular space  for  a  cell  lumen. 
Dandeno  (1906)  states  that 
the  mycelium  is  intercellular, 
but  that  small  threads  enter 
the  cells  and  even  pass 
through  them  (Fig.  31). 

Leaves. —  The   lesion    pro- 
duced on  the  leaf  is  largely 
necrotic.     The    cells    are 
brown,    collapsed,    and    ob- 
viously dead.     The  average 
thickness     of     the     normal 
apple    leaf    is    about    142  fj,, 
whereas  that  of  the  diseased 
area  is  about  61 /x  (Fig.  32). 
The  epidermal  cells  of  the  affected  tissue  are  flattened  and  bear  little 
resemblance    to   normal    epidermis.     The   palisade    cells   maintain   their 
relative  position  but  are  considerably  shortened.     The  cells  of  the  spongy 
parenchyma  are  shriveled  and  irregular  in  fonn  (Fig.  32;. 

In  some  cases  the  lesions  are  limited  by  a  vein,  and,  although  a  small  vein 
may  mark  the  extent  of  the 
diseased  area,  the  larger  veins 
more  frequently  act  in  this 
capacity.  In  cases  in  which 
the  edge  of  the  spot  does  not 
fall  at  a  vein,  a  plate  of  cells 
surrounds  the  lesion  and  limits, 
for  a  time  at  least,  the  extent 
of  the  fungus. 

The  structure  of  the  leaf  at      ^ ,  ,.        ,   .          n^,    ^.    .    . 

Showing  healthy  and  diseased  tissue.     The  beginning  of 
the    margin    of    a    spot    is    very     the  subenzed  layer,  represented  by  heavy-walled  cells  in  a 
°  '^  line  from  epidermis  to  epidermis,  should  be  noted 

different     from     either    the 

healthy  or  the  dead  parts.    The  process  of  differentiation  apparently  takes 

place  in  considerable  advance  of  the  fungus.     In  some  stained  sections 


HISTOLOGICAL   CHANGES  IN  THE  FRUIT  OF 
APPLE 

Showing  appearance  of  healthy  tissue  at  left  and  diseased 
issue  at  right,  and  the  mycelial  relationship  to  the  host  cells 


Fig.  32. 


HISTOLOGICAL     CHANGES     IN     DISEASED 
LEAF    TISSUE 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits     hi 


a  row  of  cells  with  dark-stained  walls  is  seen  in  the  leaf  (Fig.  32). 
They  are  arranged  in  a  direct  line  from  the  upper  to  the  lower  epi- 
dermis. This  involves  the  palisade  cells  and  the  spongy  parenchyma, 
the  latter  tissue  now  being  composed  of  more  densely  packed,  but  large, 
cells.  With  the  advance  of  the  fungus  this  layer  increases  in  size  and 
number  of  cells  until  the  diameter  is  increased  over  that  of  the  normal 
part.  An  additional  layer  of  palisade  cells  may  be  developed  in  this 
region,  but  in  a  late  stage  the  entire  mesophyll  becomes  densely  filled 
with  large,  irregularly  shaped  cells.  The  elongated  palisade  cells  are 
completely  changed  and  become  isodiametric  in  form.  The  apparent 
stimulation  results  in  hyperplasia  and  metaplasia  of  the  palisade  cells 
and  in  hyperplasia  of  the  spongy  tissue  (Fig.  33). 

The  diseased  cells  give  a  test  for  suberin  with  chlor-iodide  of  zinc  and 
with  cyanine-glycerin.  Certain  stages  in  the  development  of  the  leaf  spot 
show  discoloration  of  the  epi- 
dermal cells  up  to  the  suber- 
ized  layer  only.  Later,  how- 
ever, the  epidermal  cells  are 
affected  beyond  this  region, 
as  evidenced  by  their  loss  of 
normal  size  and  color.  It  ap- 
pears that  penetration  of  the 
temporary  layer  is  accom- 
plished by  the  fungus  invading 
the  epidermal  cells  and  thence 
advancing  into  the  healthy 
tissue.  At  any  rate  the  my- 
celium is  found  in  the  epidermal  cells  in  this  region.  The  alternate  pro- 
cesses of  the  formation  of  this  layer  of  tissue,  and  the  subsequent  invasion 
of  the  tissvie  beyond  the  suberized  layer  by  the  parasite,  give  rise  to  the 
concentric  rings  previously  described. 

Bark. —  The  tissues  of  the  normal  apple  stem  represent  the  condition 
found  in  a  typical  dicotyledonous  plant.  In  the  center  is  the  pith, 
radiating  from  which  region  are  alternate  medullary  rays  and  fibrovascular 
bundles.  Outside  these  is  a  C3^1inder  of  secondary  cortex,  which  is  in 
turn  surrounded  by  a  cylinder  of  thick-walled  cortex  (probably  primary 
in  nature)  and  one  of  cork  or  periderm.  In  older  stems  the  epidermis 
is  not  present.  The  secondary  cortex  is  composed  of  several  layers  of 
phloem,  in  turn  made  up  of  hard,  or  lignified,  sclerench^-ma  fibers,  sieve 
tubes,  companion  cells,  and  phloem  parencyhma.  In  a  longitudinal  sec- 
tion the  medullary  rays  are  prominent  and  are  perpendicular  to  the 
periderm.     In  the  secondary  cortex  these  rays  are  connected  by  rows  of 


Fig.    33.      HISTOLOGICAL     CHANGES     IN     DISEASED 
LEAF    TISSUE 

Showing  the  reactions  of  the  host  along  the  margin  of 
the  lesion.  Metaplasia  and  hyperplasia  are  exhibited  in  the 
mesophyll 


112  Bulletin  37c)  j 

phloem  parenchyma  which  are  oriented  at  right  angles  to  the  direction 
of  the  medullary  rays.  These  phloem  parenchyma  cells  are  rectangular 
and  similar  to  the  medullary  ray  cells;  the  arrangement  of  the  former 
results  in  the  noticeable  stratification  of  the  secondary  cortex. 

The  material  for  comparative  study  of  healthy  and  diseased  tissues 
was  usually  taken  so  that  both  areas  would  appear  in  the  same  section. 
Cankers  from  natural  and  artificial  infection  were  fixed  in  Gilson's  fixer 


Fig.  34.      HISTOLOGICAL  CHANGES  IN  DISEASED  WOOD 

Two  apple  twigs,  showing  cankers  as  they  appear  on  surface.     The  specimens 
on  the  right  are  the  same  twigs,  with  bark  removed  to  show  the  streak 

or  in  chrom-acetic  acid,  hardened  in  the  usual  manner,  and  finally  imbedded 
in  either  celloidin  or  collodion.  Sections  made  from  such  material,  as 
well  as  from  fresh  tissue,  were  cut  with  a  desk  microtome  and  stained 
with  the  following  stains:  safranine  and  methyl  blue;  safranine  and 
methyl  green;  phloroglucin ;  and  a  chlorophyll  solution. 

In  the  normal   tissues  the  lignified  and  suberized  tissues  —  that   is, 
cork  and  hard  sclerenchyma  fibers — are  stained  red  with  safranin,  whereas 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits 


13 


the  cellulose  tissues,  cortical  and  medullary,  are  colored  blue  with  methyl- 
blue  and  unstained  with  methyl-green.  The  woody  parts  stain  red  with 
phloroglucin.  In  the  diseased  part  there  is  a  very  prominent  general 
brownish  deposit,  located  chiefly  in  the  medullary  ray  cells,  the  thick-walled 
cortical  parenchyma,  and  the  phloem  parenchyma.  Such  cells  are  not 
stained  by  any  of  the  stains  used.  The  sclerenchyma  fibers  and  the  cork 
are  colored  red  by  saf- 
ranine,  whereas  suberized 
cork  cells  are  made 
green  with  a  chlorophyll 
solution.  Diseased  wood 
shows  a  test  for  lignin 
phloroglucin. 

The  more  striking  ex- 
ternal symptoms  of  the 
canker  noted  are  the  dis- 
coloration of  the  bark,  a 
crevice  at  the  margin  of 
the  lesion,  and  a  sinking 
of  the  tissues.  It  has  been 
noted  elsewhere  that  the 
organism  penetrates  the 
wood  to  a  limited  extent 
only,  so  that  the  more 
notable  changes  occur  in 
the  bark.  The  canker  is 
sometimes  superficial,  the 
attacks  of  the  organism 
being  confined  to  the  cor- 
tical tissues.  Attacks  on 
the  wood  of  old  limbs  are 
not  frequent,  but  on  twigs 
the  wood  is  subject  to 
common  invasion  by  the 
parasite.  In  cross  and  lon- 
gitudinal sections  the  first  and  the  second,  and  sometimes  the  third, 
layers  of  wood,  and  even  the  pith,  are  discolored.  Closer  examination 
shows  the  mycelium  to  be  very  abundant  within  the  vessels  of  the  xylem 
and  in  the  woody  parenchyma,  In  this  region  the  characteristic  brown 
deposit  is  found,  but  is  located  chiefly  in  the  cells  of  the  medullary 
rays  and  the  wood  parenchyma.  Inoculations  on  young  apple  trees  in 
the  greenhouse  with  the  ascospore  strain  (no.  82,  from  apple)  show  that 


Fig.  35.      HISTOLOGICAL  CHANGES  IN  DISEASED  WOOD 

Cross  section  of  part  of  apple  twijj,  showing  brown  deposit  in 
wood  fibers  and  wood  parenchyma  cells.  Mycelium  is  also  shown 
in  the  xylem  ducts,  but  it  should  be  noted  that  none  is  found 
in  other  woody  elements 


114 


Bulletin  379 


there  is  a  streak  developed  in  the  outer  layers  of  wood  (Fig.  34),  just  as 
in  the  twig  blight  on  chestnut  oak,  Quercus  prinus,  as  reported  by  Ingram 
(19 1 2)  and  noted  subsequently  by  Rankin  (1914)-  The  streak  is  due  to 
the  discoloration  of  the  cells,  not  to  the  presence  of  the  rnycelium 
(Figs.  35  and  36).  One  has  only  to  examine  longisections  through  the 
streak  to  be  convinced  that  the  hyphal  threads  do  not  grow  in  strands 
and  are  not  otherwise  arranged  so  as  to  give  such  an  appearance  to  the 
tissue. 

In  the  case  of  the  more  superficial  cankers  the  ingress  of  the  fungus  is 
cut  off  from  the  healthy  tissue  by  the  development  of  a  cork  layer  (Fig.  3  7) . 
Such  lesions  reveal  in  section  the  presence  of  a  layer  approximating  the 
normal  periderm,  with  wiiicli  it  is  continuous  and  which  reacts  the  same 

with  safranine  and  with  a  chloro- 
phyll solution.  These  cells  in  their 
final  state  are  suberized. 

The  layer  originates  by  the  di- 
vision of  cells  of  the  cortical  paren- 
chyma. The  sclerenchyma  fibers 
are  not  changed.  If  the  layer 
comes  in  contact  with  a  group  of 
sclerenchyma  fibers  it  is  inter- 
rupted .  The  more  recently  affected 
cells — that  is,   those  nearest  the 

l!\'i'  \  Hill1lMll\\MMllWPVIMlll     ^'"3-rgi^  of  the  lesion — show  a  red- 

IfyiiiV  "f  ^v|S\\\iI™IMi\mMiIwK^^^^  dish  tinge  with  safranine,  indi- 
cating slight  suberization  through- 
out the  region.  Later,  evidence 
of  the  cork  layer  is  found  just 
beyond  the  infected  zone.  Walls 
are  laid  down  to  form  rectangular  cells  characteristic  of  the  final 
cork  layer  and  of  the  normal  periderm.  At  this  time  they  do  not  take 
the  safranine,  indicating  that  suberization  has  not  begun.  Such  sections 
stained  with  chlorophyll  solution  also  show  no  suberin  reaction. 

A  later  examination  of  the  marginal  layer  between  healthy  and  diseased 
tissue  stained  with  safranine  will  reveal  three  distinct  and  characteristic 
zones,  as  follows  (enumerating  entad) :  a  red  layer  of  three  or  four  suberized 
cork  cells;  a  colorless  layer  of  about  two  non-suberized  cells,  rectangular; 
and  a  third  layer  of  about  two  smaller  cells  of  the  same  shape  bearing  a 
brownish  deposit,  making  a  distinct  brown  line.  Many  slides  show  the 
reverse  relation  with  respect  to  the  suberized  and  cellulose  layers;  the 
colorless  layer,  composed  of  cells  with  cellulose  walls,  may  lie  next  to  the 
diseased  tissue,  and  the  cells  with  suberized  walls  next  to  the  brown  line. 


36.         HISTOLOGICAL      CH.A.NGES 
DISEASED    WOOD 

Longisection  of  a  part  of  apple  twig,  showing 
brown  deposit  in  woody  elements.  Mycelium  is 
again  to  be  seen  in  the  xylem  ducts 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits     115 


This  raises  the  question  as  to  which  cells  are  suberized  first.  The  assump- 
tion is  that  those  cells  nearest  the  diseased  zone  are  suberized  first.  This 
would  be  expected,  in  such  a  case,  where  response  to  injury  is  made  by  the 
host.  But  this  scarcely  explains  the  cases  in  which  the  colorless  layer 
borders  the  affected  tissue.  In  these  cases,  however,  the  brown  line 
is  not  so  distinct  as  described  above,  and  often  is  not  in  evidence ;  so  that 
this  may  stand  as  a  younger  stage  in  the  formation  of  the  cork  layer. 
The  cells  of  the  suberized  layers  do  not  react  alike  when  stained  with 
safranine.  A  row  of  cells  in  the  center  is  the  darkest,  the  color  shading 
off  on  both  sides,  perhaps 
indicating  the  amount  of  ^p^^r^g^j^j 
suberi-zation.  ''    "  '^ 

The  majority  of  the  cells 
of  the  layer  are  densely 
granular,  are  thin-walled 
at  first,  and  possess  large 
nuclei.  These  have  the 
characteristics  of  rapidly 
dividing  cells. 

A  section  through  a 
canker  having  a  crevice  at 
its  margin  shows  that  the 
break  follows  the  brown 
line.  The  dead  tissues  on 
the  one  hand  shrink,  while 
the  living,  normal  part  in- 
creases in  diameter  by 
growth,  exerting  tension  on 
all  tissues  of  the  bark,  and 
the  break  results.  It  ap- 
pears that  the  cells  making 
up  the  brown  line  are  the 
weakest,  and  thus  they  mark  the  line  of  separation  of  the  diseased 
from  the  healthy  tissue. 

Along  the  marginal  layer  diseased  pockets  occasionally  are  formed  which 
extend  into  the  healthy  tissue.  Such  areas  are  always  in  the  region  of  a 
group  of  sclerenchyma  fibers.  A  cork  layer  surrounds  the  pocket.  Cross 
sections  may  be  cut  so  as  to  include  only  a  portion  of  one  of  these  pockets, 
making  them  appear  as  internal,  separate  infections.  Serial  sections, 
however,  always  reveal  their  connection  with  the  originally  infected  tissue. 

In  the  diseased  region  are  found  the  same  stratified  layers  as  mentioned 
in  the  survey  of  the  nonnal  secondary  cortex.     But  in  the  affected  areas 


Fig.  37. 


HISTOLOGICAL      CHANGES     IN     DISEASED 
BARK 

Showing  brown  deposit  in  the  medullary  ray  cells  and 
phloeni  parenchyma,  which  cross  at  right  angles  resulting  m 
a  stratified  appearance  in  the  phloem.  Below  the  diseased 
region  is  seen  the  cork  layer 


ii6  Bulletin  379 

both  the  cells  of  the  medullary  rays  and  the  phloem  parenchyma  stand 
out  very  prominently,  being  filled  with  the  brownish  deposit.  The 
remainder  of  the  old  phloem  elements,  the  sieve  tubes,  companion  cells, 
and  sclerenchyma  fibers,  are  not  discolored  at  all.     (Fig.  37.) 

The  brown  mycelium  of  the  fungus  is  found  very  abundantly  throughout 
the  diseased  area.  It  is  intercellular,  except  when  it  encounters  the  xylem 
and  the  hard  sclerenchyma  fibers;  it  is  not  easy  to  say  just  what  the 
relationship  is  with  respect  to  hard  sclerenchyma  fibers.  It  is  noted  else- 
where that  the  hyphae  are  found  within  the  tracheal  tubes.  The  threads 
for  the  most  part  pass  up  and  down  the  stem.  This  is  in  accordance  with 
the  external  symptoms  of  a  lesion.  It  has  been  stated  previously  that 
where  the  cork  layer  encounters  a  group  of  sclerenchyma  fibers  it  is  inter- 
rupted, and  the  fungus  breaks  through  the  barrier  as  laid  down  by  its 
host.  There  is  no  evidence  that  the  suberized  cells  are  ever  penetrated. 
Mycelium  is  found  advancing  through  the  layer  at  points  where  the 
sclerenchyma  fibers  cross  it,  a  discoloration  precedes  the  hyphas,  and 
almost  before  the  threads  get  into  the  -healthy  tissue  the  latter  is  changed 
in  its  normal  color.  Very  soon  after  is  found  evidence  of  a  secondary 
cork  layer,  which  usually  branches  from  the  primary  layer  at  some  point 
beneath  the  point  of  secondary  penetration.  This  extends  around  the 
newly  afTected  region,  finally  passing  above  to  the'  normal  periderm. 
Repetition  of  this  process,  accompanied  by  the  formation  of  crevices  at 
each  successive  cork  layer,  results  in  the  concentric  lines  or  cracks  so 
characteristic,  externally,  of  the  lesion.  The  drying  out  and  death  of  the 
cells  results  in  their  collapse,  and  the  affected  part  shrinks. 

CONTROL 

BLACK  ROT 
EXCLUSION  BY  LEGISLATION 

As  previously  noted  (Evans,  19 10),  the  British  Government  at  Cape 
Colony  has  legislated  against  black  rot.  Importers  are  warned  that, 
under  a  government  notice  of  1908,  all  consignments  of  pomaceous  fruits 
found  infected  with  this  organism  to  the  extent  of  one  per  cent  and  upward 
will  be  destroyed  on  arrival  at  the  Colony  or  returned  to  the  consignor. 

SPRAYING 

It  was  suggested  by  Sturgis  (1893  b)  that  spraying  in  August  and 
September  would  prevent  black  rot  of  quince.  The  following  year  the 
same  author  (1894)  found  that  a  0.03-per-cent  solution  of  copper  sulfate 
is  fatal  to  the  fungus.  More  recently  Waite  (1906:19)  recommends  the 
same  treatment  as  for  apple  scab.  Wolf  (19 13)  concludes  from  experi- 
ments conducted  in  Alabama  that  bordeaux  4-4-50,  applied  as  follows, 
will  be  effective:    the  first  spraying,  about  July  15,  when  the  disease  is  just 


Black  Rot,  Leap  Spot,  and  Canker  of  Pomaceous  Fruits     117 

appearing;  the  second,  two  weeks  later.  This  schedule  gave  satisfactory 
control,  the  sprayed  fruits  showing  less  than  one  per  cent  diseased  on 
certain  varieties.  Control  was  less  complete  on  Black  Ben  Davis,  which 
exhibited  from  ten  to  fifteen  per  cent  of  black  rot.  Lime-sulfur  was  found 
to  be  wholly  ineffective  under  southern  conditions  in  191 2. 

It  should  be  remembered  that  frequently  infections  follow  the  work  of 
the  codling  moth,  and,  as  stated  by  Clinton  and  Britton  (1910),  the 
control  of  this  insect  lessens  the  amount  of  rot  starting  at  such  centers. 
The  work  heretofore  described  indicates  that  certain  insects  carry  the 
spores;  it  is  therefore  important  to  consider  the  control  of  these  pests. 

HANDLIXG  OF  FRUITS 

It  is  apparent  from  the  life  history  studies  that  spores  of  the  black  rot 
organism  are  present  in  the  orchard  at  picking  time  and  are  carried  into 
storage.  It  has  also  been  learned  that  the  fungus  effects  penetration  only 
through  injured  tissue.  Consequently  one  factor  in  obtaining  apples  of 
good  keeping  quality  is  the  elimination  of  mechanical  and  other  injuries 
to  the  fruit;  the  occurrence  of  black  rot  in  storage  is  undoubtedly  connected 
with  the  handling  methods  in  use  in  the  orchard. 

STORAGE 

It  has  been  found  by  Lamson  (1902:81),  and  subsequently  by  Eustace 
(1908),  that  the  temperature  of  the  storage  room  should  be  about  31° 
to  34°  F.  (-0.5°  to  1.1°  C).  Higher  temperatures  allow  growth  of  the 
fungus.  It  is  important  to  note  that  when  apples  are  stored  in  barrels, 
about  one  week  is  required  for  the  temperature  of  the  center  of  the 
receptacle  to  become  equal  to  that  of  the  storage  room. 

LEAF  SPOT 
SPRAYING 

It  seems  that  Alwood  (1892)  was  the  first  to  advocate  the  use  of  sprays 
for  leaf  spot.  He  recommends  two  appHcations,  as  follows:  the  first, 
just  as  the  petals  have  fallen  from  the  apple,  using  bordeaux  mixture 
4-5-50;  the  second,  about  twenty  to  twenty-five  days  later.  The  recom- 
mendations of  later  writers  differ  in  number  of  applications  and  in  type 
of  fungicide.  It  is  very  apparent  that  the  nrmiber  of  sprayings  in  a  given 
year  will  depend  on  the  character  of  the  season.  Ordinarily  two  or 
three  applications  are  necessary,  according  to  Brooks  (1909,  and  191 2, 
a  and  b)  and  others.  In  certain  seasons  of  considerable  rainfall  additional 
sprayings  may  be  necessary. 

As  previously  noted,  in  some  districts  at  least  the  leaves  are  infected 
shortly  after  they  unfold  from  the  bud,  and  infections  may  continue  through- 
out the  spring  according  to  Brooks  (1909:124).  Later  Brooks  and  De- 
Meritt  (191 2 :  188)  conclude  that  the  period  of  infection  extends  throughout 


ii8  Bulletin  379 

the  middle  of  the  summer.  The  number  of  applications  then  to  be  made 
will  depend  on  the  character  of  the  season  and  the  abundance  of  spores 
present. 

In  some  sections  of  the  country?-  where  apple  scab  also  is  to  be  combated, 
the  regular  scab  sprayings  have  been  generally  recommended  as  sufficient. 
These  are  given  by  Wallace  (1913:589-590)  as  follows:  the  first,  when 
the  blossoms  show  pink;  the  second,  after  the  blossoms  fall;  the  third, 
two  or  three  weeks  later.  If  later  scab  sprayings  are  necessary,  the 
leaf  spot  will  be  controlled.  Scott  (1906:33)  states  that  the  disease 
may  be  controlled  in  connection  with  the  treatment  for  bitter  rot;  for 
the  latter  disease  he  recommends  from  four  to  six  applications  of  bordeaux 
mixture,  made  at  intervals  of  two  weeks  beginning  about  six  weeks  after 
the  trees  blossom. 

Apparently  bordeaux  mixture  has  been  most  commonly  employed 
for  leaf  spot.  Brooks  (191 2  b:  15)  maintains  that  it  is  the  most  effective 
fungicide  for  apple  diseases,  but  points  out  that  an  objection  to  its  use 
lies  in  the  fact  that  spotting  of  the  foliage  and  russeting  of  the  fruit  are 
likely  to  occur  if  showers  follow  its  application.  The  spots  produced  on 
the  leaves  resemble  those  caused  by  the  fungus.  For  leaf  spot  alone, 
Brooks  (page  8  of  same  reference)  finds  that  self-boiled  lime-sulfur  best 
holds  the  disease  in  check. 

Lime-sulfur  is  regarded  by  Brooks  (19 1 2  b)  as  a  satisfactory  substitute 
for  bordeaux,  and  in  a  later  publication  Brooks  and  DeMeritt  (191 2) 
show  that  commercial  lime-sulfur  at  a  strength  of  one  gallon  to  twenty-five 
gallons  of  water  reduced  the  infection  from  about  95  per  cent  to  26  per  cent. 
When  used  at  a  strength  of  one  gallon  to  fifty  gallons  of  water,  the  lime- 
sulfur  was  found  to  be  less  effective.  Brooks  considers  this  fungicide 
about  as  efficient  as  bordeaux,  and,  because  of  the  injury  from  the  latter, 
lime-sulfur  would  appear  the  more  desirable. 

CULTIVATION 

Brooks  and  DeMeritt  (19 12)  have  observed  marked  contrast  between 

the  amount  of  infection  in  sod  and  in  cultivated  orchards.     They  record 

the  former  as  showing  0.79  spot  per  leaf,  whereas  in  the  latter  there  was 

only  0.47  spot  per  leaf.     They  say  (page  189  of  reference  cited) : 

The  trees  had  been  treated  alike  in  every  other  respect  and  wgre  of  equal  vigor  when 
the  experimental  work  was  begun ;  it  was,  therefore,  evident  that  cultivation  had  reduced 
the  disease  almost  one-half.  This  reduction  was  probably  partly  due  to  the  fact  that  the 
leaves  were  plowed  under  on  the  cultivated  plots,  but  the  lack  of  general  vigor  in  the 
trees  on  the  sod  plots  was  apparently  partly  responsible  for  the  difference. 

CANKER 
HISTORICAL  AND  INTRODUCTORY 

The  control  of  cankers  has  been  a  matter  of  consideration  for  some  time. 
Nearly  three  centuries  ago  Parkinson  (1629:550)  recommended  surgical 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits    119 

methods  together  with  a  wound  dressing  of  vinegar.  Similar  advice  is 
given  by  Harrison  (1823:342),  who  suggests  a  dressing  of  soot,  water, 
and  train  oil.     He  recommends  drainage  of  the  soil  in  severe  cases. 

In  more  recent  times,  beginning  with  the  appearance  of  the  work  of 
Paddock  (1899  b),  the  recommendations  are  all  essentially  of  the  same 
nature.  The  employment  of  the  common  methods  of  orchard  manage- 
ment —  cultivation,  fertilization,  pruning,  and  spraying  —  is  recom- 
mended, in  order  to  promote  general  vigor.  Keeping  the  trees  in  good 
growing  condition  is  claimed  to  be  essential  (Warren  and  McCourt,  1905). 
Spraying  to  protect  the  bark  is  frequently  recommended  (Bethune,  1909 :  30, 
and  others),  while  scraping  the  bark  and  applying  a  wash  is  suggested 
by  Paddock  (1899  b:  190)  and  others.  Pruning  of  diseased  limbs  and 
the  growing  of  a  new  top  is  being  practiced  by  some  growers. 

The  control  measures  more  commonly  employed  by  the  growers  of 
New  York  State  are  pruning  and  spraying;  other  measures,  as  determined 
by  circular  letters  and  personal  observation,  are  surgery/,  cultivation, 
fertilization,  and  mulching.  The  success  of  these  methods  varies  and 
seems  to  depend  on  the  vigilance  with  which  the  grower  pursues  the 
disease. 

surgical  methods 

PRUNING.  In  pruning  for  the  control  of  canker,  two  methods  may 
be  employed:  the  limb  may  be  cut  from  the  tree  entirely,  or  the  cankered 
bark  may  be  removed.  In  either  case  a  wound  will  result  and  the  appli- 
cation of  a  dressing  becomes  essential. 

Removal  of  limbs.—  The  question  frequently  arises,  when  shall  only 
the  canker  be  cut  out,  and  when  is  it  necessary  to  remove  the  limb?  No 
general  rule  can  be  laid  down,  but  each  case  must  be  examined  carefully 
and  procedure  taken  accordingly.  If  the  limb  is  large  and  productive, 
its  removal  should  be  postponed.  This  is  commonly  the  practice.  But 
to  wait  until  the  limb  is  not  producing  satisfactorily  usually  means  that 
the  canker  will  aid  in  bringing  the  branch  to  destruction.  In  such  cases 
it  is  advisable  to  prevent  the  loss  by  eradicating  the  cankered  spot  by 
surgery. 

If  the  limb  is  not  producing,  whether  large  or  small,  its  removal  for 
the  purpose  of  eliminating  the  fungus  is  the  alternative.  The  cut  should 
be  made  so  that  another  limb,  or  water  sprout,  may  be  allowed  to  grow 
in  the  approximate  space  left  by  the  part  removed.  This  method  of 
treating  the  New  York  apple  tree  canker  is  employed  in  certain  orchards 
along  the  Lake  Ontario  belt  in  this  State.  One  grower  is  very  successful 
in  this  measure  of  control.  This,  with  protection  from  new  infections 
by  careful  spraying  of  the  entire  tree  —  trunk  and  limbs  —  renders  even 
the  highly  susceptible  Twenty  Ounce  variety  practically  free  from  canker. 


I20  Bulletin  379 

Grafting  of  stubs  left  by  the  pruning  of  the  affected  parts  of  limbs 
is  occasionally  practiced.  This  may  be  justified  in  certain  cases,  although 
as  a  rule  it  should  be  supplemented  in  the  main  by  the  method  just 
described. 

Removal  of  diseased  bark. —  The  cutting  out  of  cankers  is  a  method 
to  be  employed  when  the  grower  is  satisfied  that  the  value  of  the  limb 
warrants  it.  An  attempt  to  remove  all  kinds  and  sizes  of  cankers  from  an 
infested  orchard  without  regard  to  such  a  consideration  is  likely  to  result 
in  the  discouragement  of  the  orchardist  with  the  whole  undertaking. 
The  equipment  necessary  for  use  in  the  removal  of  cankered  bark  consists 
of  a  drawshave  and  a  farrier's  knife.  The  limits  of  the  diseased  area  are 
ordinarily  determined  by  making  an  external  examination  of  the  canker. 
Where  this  method  is  not  reliable,  small  bits  of  the  outer  bark  may  be 
removed,  following  the  line  of  the  discoloration  until  the  limits  are  deter- 
mined.    Similarly  the  depth  of  the  canker  is  defined. 

The  shape  of  the  cut  will  vary  somewhat  with  that  of  the  canker  to  be 
removed.  So  far  as  possible,  the  wound  when  finally  finished  should  be 
lenticular  in  form.  This  will  facilitate  callus  formation.  If  the  wound  is 
rectangular  the  upper  and  lower  edges  heal  more  slowly.  The  edge  of 
the  wound  should  be  perpendicular  to  the  long  axis  of  the  limb,  for  cuts 
made  at  a  slant  will  result  in  a  certain  amount  of  dead  cortex,  which  is 
undesirable  from  the  standpoint  of  new  infections.  A  possible  exception 
to  this  method  of  trimming  the  margin  is  to  be  found  at  the  lower  end 
of  the  wound.  Here  the  edge  should  be  slanting  enough  to  permit 
drainage  of  moisture. 

WOUND  TREATMENT.  It  is  frequently  advised  that  the  wound  should 
be  disinfected  and  protected.  The  latter  is  certainly  commendable 
practice,  but  whether  the  former  is  necessary  will  depend  on  the  nature 
of  the  wound  dressing. 

Wound  disinfection. —  If  the  dressing  itself  is  a  disinfectant,  a  special 
disinfectant  will  not  be  necessary.  In  case  one  is  needed,  mercuric 
chloride  at  the  usual  strength  (i-iooo),  or  copper  sulfate  (i  ounce  to  i 
gallon  of  water),  is  most  commonly  used. 

Wound  protection. — ■  The  necessity  of  a  protective  covering  for  wounds 
is  twofold :  to  check  the  weathering  of  the  wound,  and  to  prevent  the  growth 
of  bacteria  and  fungi.  It  follows,  then,  that  the  fundamental  requirement 
of  a  vvound  dressing  is  that  it  should  be  a  preservative  and  a  pre- 
ventive. Briefly,  then,  the  dressing  should  have  antiseptic  qualities,  and 
should  be  fluid,  reasonably  inexpensive,  and  easily  prepared  and  applied; 
it  is  essential  that  it  should  give  complete  covering;  it  must  be  impervious 
to  air  and  water,  must  be  durable,  and  must  not  injure  nor  kill  the 
tissues  nor  interfere  with  the  healing  process. 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits     121 

The  preparations  now  most  cornmonly  used  are  paint,  tars,  and 
asphaltum.  In  some  cases  commercial  tree  paints  are  employed.  It  is  gen- 
erally agreed  that  paints  are  an  inefficient  covering,-  whereas  asphaltiim 
once  applied  gives  the  desired  protection.  Asphaltum,  however,  is  more 
difficult  to  apply.  This  is  particularly  true  if  the  asphaltum  used  is 
rendered  liquid  by  heat;  if  it  is  dissolved  in  gasoline  it  is  more  easily  pre- 
pared and  hence  more  available.  The  combination  of  asphaltum  and 
gasoline  has  been  applied  rather  extensively  in  the  orchard  of  Fred  Hazle- 
ton,  at  Leroy,  New  York,  and  from  all  appearances  is  commendable. 

The  writer  has  used  coal  tar  for  the  past  three  years  with  good  success. 
This  is  a  residual  tar  derived  in  the  manufacture  of  artificial  gas  from  coal. 
According  to  Lunge  (1909),  tars  may  vary  even  from  the  same  materials, 
depending  on  the  temperature  used  in  the  distillation,  the  shape  of  the 
retort,  and  other  factors.  The  use  of  coal  tar  as  a  wound  dressing  has 
been  recommended  to  growers  of  the  State,  and  some  have  complained  of 
injury  to  the  healthy  tissue  from  its  use  while  others  report  it  as  an  appro- 
priate material.  Many  cases  of  injury  have  been  found  to  have  resulted 
from  the  use  of  creosote,  but  not  from  coal  tar.  The  pruner  must  dis- 
tinguish between  the  two  materials.  The  writer  has  never  seen  any  cases 
of  injury  from  coal  tar  on  apple  trees,  and  it  has  been  used  successfully 
on  peaches  by  Jehle  (19 13).  It  is  interesting  to  note  a  quotation  from 
Des  Cars  as  given  by  Bailey  (1907:111-113): 

The  application  of  coal  tar  should  not  be  made  except  with  considerable  caution 
in  the  treatment  of  wounds  on  drupaceous  fruits  (cherries,  peaches,  plums,  etc.),  and 
especially  on  the  plum  tree.  It  has  often  been  observed  that  the  bark  of  fruit  trees 
of  this  class  has  suffered  from  the  application  of  coal  tar.  This  is  not  the  case,  however, 
with  pome-bearing  trees  (apples,  pears,  etc.);  to  these  coal  tar  may  be  appUed  with 
perfect  safety. 

Card  (1897  : 9)  reports  experiments  in  pruning  in  which  he  tested  various 
materials  for  protecting  wounds.  He  says  of  coal  tar:  "  Coal  tar,  how- 
ever, seems  to  have  been  a  positive  hindrance  to  the  healing  process,  not 
one  wound  having  been  reported  as  healing  extremely  well,  while  the 
majority  are  reported  as  heaHng  only  fairly  well."  As  a  comment  on  this 
remark,  Bailey  (1907 :  113)  says:  "  It  is  not  said,  however,  whether  the  tar 
injured  the  tissues,  or  whether  the  apparent  results  may  not  have  been 
due  to  the  position  and  character  of  the  wound  quite  as  much  as  to  the 
dressing.     In  my  own  experiments      ....      tar  did  no  damage." 

In  view  of  the  complaints  made  of  injury  from  the  use  of  coal  tar,  it 
occurred  to  the  writer  that  this  substance  varied  sufficiently  in  different 
parts  of  the  State  to  account  for  the  injury,  if  any  ever  occurred.  Samples 
were  obtained  from  the  gas  plants  in  the  following  cities  in  New  York: 
Syracuse,  Owego,  Batavia,  Rochester,  Ithaca,  Lockport,  Buffalo,  Albion, 
and  Geneva.     These  samples  were  applied  to  wounds  of  mature  apple 


122  Bulletin  379 

trees  on  the  fann  of  Dr.  Johnson,  at  Leroy,  New  York,  in  August,  191 2. 
Examination  at  intervals  during  the  growing  seasons  of  19 12  and  19 13 
showed  equally  good  healing  and  no  injury.  Another  orchard,  near 
Batavia,  New  York,  owned  by  Chapin  &  Son,  has  been  extensively  treated 
with  coal  tar,  with  results  similar  to  those  just  described.  The  writer  has 
applied  coal  tar  to  Northern  Spy,  Baldv/in,  and  Hubbardston  apples  in 
an  orchard  at  Byron,  New  York,  and  no  detrimental  effects  have  been 
observed.  In  some  cases  the  wound  has  been  disinfected  by  the  use  of 
mercuric  chloride  (i-iooo),  but  no  difference  in  the  efficiency  of  protection 
was  observed  between  wounds  so  treated  and  those  not  disinfected.  The 
writer  feels  safe  in  recommending  the  use  of  coal  tar  without  previously 
disinfecting  the  wounded  surface. 

The  cost  of  canker  treatment  —  that  is,  the  removal  of  diseased  bark 
and  the  application  of  a  dressing  —  is  not  an  easy  matter  to  determine. 
Where  it  is  done  extensively  the  grower  usually  does  the  work  along  with 
the  regular  pruning,  so  that  the  cost  of  canker  treatment  alone  can  hardly 
be  separated  from  that  of  the  whole  operation.  In  an  apple  orchard  at 
Leroy,  New  York,  careful  work  was  done  in  191 2  by  A.  S.  Davis.  The 
orchard  contained  950  forty- years-old  trees.  The  orchard  had  been 
neglected  for  several  years,  and  dead  limbs,  cankers,  collar  rot,  and  heart 
rot  were  abundant.     Mr.  Davis  furnishes  the  following  figures: 

Cost  of  trimming $407  .  90 

Coal  tar,  40  gallons,  at  20  cents  a  gallon 8.00 

Corrosive  sublimate .75 

Applying  tar 30 .  00 

Removal  and  destraction  of  brush 54  •  70 

Total  $501 .35 


The  following  data  are  taken  from  a  similar  orchard  at  Batavia,  New 
York: 

Miscellaneous  data 

Number  of  trees 360 

Age  of  trees 30  yeai-s 

Cost 

Labor,  348  hours,  at  25  cents  an  hour $87  .00 

Coal  tar,  10  gallons,  at  15  cents  a  gallon i  .50 

Corrosive  sublimate .50 

Total $89 .  00 


It  is  seen  that  the  average  cost  of  the  work  in  the  Leroy  orchard  is 
about  fifty-two  cents  a  tree.     It  must  be  borne  in  mind  that  the  orchard 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits     123 

had  not  been  pruned  in  several  years,  which  accounts  in  part  for  the 
high  cost  of  the  work.  In  the  Batavia  orchard  the  average  cost  is  approx- 
imately twenty-five  cents  a  tree.  These  figures  do  not  represent  the  cost 
of  treating  the  cankers  alone;  this  process  itself  would  be  considerably 
less  than  either  of  the  above  figures. 

WOUND  HEALING.  Wouud  cork. —  According  to  Hartig  (1894:225), 
whenever  the  living  phellogen  is  injured  a  new  zone  of  phellogen,  or 
cork,  which  is  continuous  with  the  cork  layer  along  the  edge  of  the  wound , 
is  formed  from  the  uninjured  cells  which  are  situated  deeper  in  the 
cortex.  The  cortical  parenchyma,  which  lies  beneath  the  periderm, 
possesses  sufficient  power  of  cell  division  to  enable  it  to  keep  pace  with 
the  increasing  thickness  of  the  stem.  But  in  the  case  of  the  wound  its 
reproductive  capacity  is  confined  to  the  development  of  a  periderm  close 
beneath  the  surface  of  the  exposed  tissues.  Its  formation  does  not  depend 
on  the  season  of  the  year,  but  it  may  be  formed  even  in  winter. 

Wound  wood. —  Hartig  (1894:228)  states  that  wood  exposed  by  a 
wound  has  the  power  of  producing  new  cortex  and  new  wood  when  the 
cambium  is  active  and  when  the  cambium  layer  and  young  wood  are 
protected  from  drought.  In  such  a  case,  regeneration  of  the  covering 
layers  is  effected.  The  cambial  region  consists  of  embryonic  bast  and 
wood,  which  is  capable  of  growth  and  ultimately  of  a  certain  amount 
of  differentiation.     The  wood  thus  formed  is  termed  wound  wood. 

Calhis. —  Callus  may  be  developed  when  the  cambium  has  dried  up 
or  when  it  is  absent  from  the  surface  of  the  wound.  Its  formation  proceeds 
from  the  edge  of  the  wound,  beginning  in  the  cambium.  Hartig  (1894: 
231)  states  that  it  is  a  purely  mechanical  process  and  results  from  the 
reduction  of  the  bark  pressure  on  these  tissues.  Theje  is  always  a  certain 
amount  of  tension  in  the  cortical  mantle,  whereby  a  considerable  pressure 
is  exerted  on  the  cambium.  Should  this  pressure  be  locally  reduced  by 
a  wound's  reaching  the  wood,  the  processes  of  cell  division  and  growth 
are  accelerated  not  only  along  the  edges  of  the  wound  but  also  at  greater 
distances.  The  callus  cushions  advance  from  the  edges  oi  the  wound, 
finally  coming  in  contact  and  coalescing.  This  coalescence  is  retarded 
if  the  callus  is  clothed  at  an  early  stage  with  dead  bark. 

It  has  been  noted  that  wounds  made  in  cutting  out  cankers  should  be 
pointed  in  order  to  permit  rapid  healing.  In  this  connection  Hartig 
(1894:232)  states  that  the  formation  of  callus  proceeds  more  vigorously, 
in  case  of  a  longitudinal  incision  than  when  the  incision  is  transverse. 
This  is  explained  by  the  nature  of  the  pressure  by  the  bark  in  consequence 
of  peripheral  enlargement  of  the  stem.  The  pressure  here  acts  like  that 
of  a  barrel  hoop  on  the  staves,  and  so  callus  develops  more  rapidly  along 
the  lateral  margins  of  the  wound.     In  this  connection  the  question  of 


124  Bulletin  379 

slitting  the  lower  edge  of  the  callus  arises.  Reasoning  from  the  data 
regarding  the  development  of  the  callus,  it  seems  advisable  to  practice 
this  operation  each  year;  this  prevents  the  callus  from  bunching,  and 
stimulates  it  to  more  ready  occlusion  of  the  wound. 

SPRAYING 

The  effectiveness  of  spraying  for  canker  is  a  question  frequently  raised. 
It  is  the  belief  of  the  writer  that  spraying  as  a  preventive,  but  not  as 
a  cure,  is  worthy  of  attention.  It  is  true,  however,  that  growers  report 
cases  of  curing  canker  by  spraying.  The  fungus  mycelium  is  protected 
by  the  bark;  hence  sprays  will  not  reach  it,  and  eradication  of  the  fungus 
from  a  given  lesion  by  spraying  seems  highly  impossible.  Spraying  to 
protect  healthy  bark  from  infections  would  certainly  appear  advisable, 
but  the  data  at  hand  are  somewhat  conflicting.  The  writer  recalls  an 
orchard  in  which  canker  does  not  occur.  The  trees  are  sprayed  carefully 
each  year,  according  to  general  recommendations  for  apples.  Some  of 
the  trees  are  Twenty  Ounce,  but  they  are  free  from  the  disease.  The 
limbs  are  kept  coated  with  spray  throughout  the  summer,  and  as  late 
as  the  middle  of  August  these  trees  are  still  covered.  In  contrast  to  this 
orchard,  another  is  recalled  which  is  severely  affected  with  canker,  yet 
the  trees  are  given  the  regular  sprayings.  The  difference  in  these-  cases 
may  be  accounted  for  by  the  lack  of  thoroughness  of  the  spraying  in 
the  second  orchard.  Since  protection  is  the  principle  involved  in  this 
method  of  control  of  canker,  the  success  of  any  attempts  in  this  direction 
is  determined  by  the  completeness  of  the  covering. 

GENERAL  CONSIDERATIONS 

The  destruction  of  rubbish  about  the  orchard  is  no  new  suggestion. 
Peck  (1879 :  2 1)  recommends  that  affected  fruit  should  be  removed  from  the 
orchard  and  destroyed.  The  destruction  of  fallen  leaves  is  recomme'nded 
by  Alwood  (1892),  Sheldon  (1905)  and  others  suggest  picking  rotted 
fruit  before  the  fungus  spores  mature  in  the  case  of  quince  black  rot; 
Sheldon  adds  that  this  might  not  be  possible  with  apples  because  of  the 
size  of  the  trees.  In  Alabama, however.  Wolf  (19 13),  as  has  been  previously 
noted,  controlled  the  disease  by  spraying.  The  opinion  is  held  by  Brooks 
and  DeMeritt  (1912:189)  that  affected  leaves  should  be  plowed  under, 
while  clean  cultivation  is  the  recommendation  of  Reed,  Cooley,  and 
Rogers  (1912:5).  The  removal  and  burning  of  affected  hmbs  is  advocated 
by  Bethune  (1909:30)  and  others. 

The  ability  of  the  fungus  to  pass  from  one  part  of  the  apple  tree  to 
another  only  adds  to  the  sources  of  inoculum,  so  that  sanitary  measures 
become  of  special  importance. 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits     125 

ORCHARD  management 

The  value  of  careful  handling  of  fruit  to  prevent  injury  has  been 
emphasized.  This  is  based  on  the  principle  that  the  causal  organism 
is  a  wound  parasite.  The  same  care  should  be  exercised  with  reference 
to  the  bark  of  the  tree;  injury  should  be  avoided  whenever  possible. 
Injuries  to  bark  are  likely  to  result  from  cultivating  implements  and 
harness,  the  careless  handling  of  ladders  while  picking,  and  climbing 
over  the  trees  with  rough-soled  boots.  The  importance  of  guarding  against 
such  orchard  practice  lies  in  the  fact  that  cankers  begin  in  just  this  sort 
of  place. 

It  has  been  mentioned  that  the  fungus  follows  winter  injury.  As 
a  protection  against  winter  injury,  Reddick  (1912:37)  advocates  early 
plowing  in  the  spring,  and  cultivation  to  give  the  trees  the  advantage 
of  conserved  moisture;  he  recommends  that  cultivation  should  cease  not 
later  than  August  i,  in  order  to  start  the  trees  into  maturation.  Cover 
crops,  to  take  up  excess  moisture  in  the  autumn,  should  be  sown.  Soil 
drainage  in  low  ground,  and  a  good  circulation  of  air,  are  important 
considerations. 

When  it  is  desired  to  grow  varieties  that  are  susceptible,  the  canker 
difficulty  may  be  obviated  to  a  considerable  extent  by  working  over  the 
larger  limbs  of  more  resistant  varieties  to  the  one  desired.  This  has 
been  done  with  apparent  success  in  a  few  instances.  The  difficulties 
involved  are  that  pruning  must  be  done  every  year  to  remove  all  sprouts 
from  the  stocks,  and  that  renewal  of  old  branches  cannot  be  effected 
so  readily.  Such  a  treatment  also  throws  the  bearing  area  higher  into 
the  air,  so  that  in  the  case  of  erect  growers,  such  as  Twenty  Ounce,  thorough 
orcha]:d  operations  are  made  more  difficult. 

RESISTANT  VARIETIES 

Since  certain  varieties  of  the  apple  —  for  example,  Esopus  and  Twenty 
Ounce  —  are  more  susceptible  to  canker  than  are  other  varieties,  the 
growing  of  other  varieties  will  undoubtedly  render  the  problem  of  control 
less  difficult.  Twenty  Ounce,  however,  is  one  of  the  most  satisfactory 
fall  varieties  for  commercial  planting  in  New  York  State.  The  question 
therefore  arises,  whether  the  orchardist  should  sacrifice  the  growing  of  this 
variety  in  the  hope  of  escaping  the  problem  of  canker  control.  The 
evidence  at  hand  indicates  that  if  a  grower  wishes  to  raise  Twenty  Ounce, 
his  success  in  keeping  the  trees  free  from  canker  will  depend  on  his  efforts. 
Observations  warrant  this  opinion.  It  is  true  that,  as  stated  by  Warren 
and  McCourt(i9o5),  "something  more  than  thrifty  growth  seems  to  be 
necessary  in  order  to  prevent  the  destruction  of  the  Twenty  Ounce"; 
so  that  vigor  in  itself  should  not  be  given  too  much  dependence.     Well- 


126  Bulletin  379 

cared-for  trees  of  this  variety  are  often  severely  cankered.  It  is  assumed 
that  the  trees  must  be  in  a  thrifty  condition  in  order  to  give  the  best 
results,  but  the  control  problem  does  not  end  here,  for  vigor  does  not  estab- 
lish nor  maintain  resistance. 

AN  ENEMY  OF  THE  PATHOGENE 

Potebnia  (1912)^  reports  an  interesting  case  of  a  fungus,  Helico- 
myces  Sphaeropsidis  Potebnia,  living  as  a  parasite  within  the  conidia  of 
Sphaeropsis  pseudodiplodia  [=  Physalospora  Cydoniae].  Infection  takes 
place  when  the  host  (the  conidia  of  Physalospora  Cydoniae)  is  in  the  Macro- 
phoma  stage.  He  notes  a  similar  case  reported  by  Japp,  in  which  Heli- 
co:nyces  niveus  Bres.  &  Japp  is  parasitic  on  Diplodia  inquinans  West., 
and  states  that  in  Japp's  herbarium  specimen  all  pycnospores  in  the 
infected  pycnidia  were  killed  by  this  parasite. 

BIBLIOGRAPHY 
(Anonymous) 

iSgga     The  app'e  canker.     Country  gent.  64:88. 

Briefly  summarizes  the  works  of  Waite  and  Paddock. 

1899  b     The  apple  canker.     Country  gent.  64:208.     Illustrated. 

The  illustration  is  a  text  figure,  and  the  author  contends  that  it  is  the  first  figure  of 
the  disease  published. 

1899  c     Perhaps  apple  canker.     Country  gent.  64:248. 

A  reply  to  an  inquiry  concerning  the  apple  injury  which  is  regarded  as  caused  by  Sphae- 
ropsis Malorum.     Remedy  suggested. 

Alderman,  W.  H.,  Giddings,  N.  J.,  and  Rumsey,  W.  E. 

1913     Orchard  spraying.     West  Virginia  Univ.  Agr.  Exp.  Sta.    Circ.  7 : 
1-48,  fig.  1-33. 

Mention  black  rot,  leaf  spot,  and  canker,  and  suggest  control  measures. 

Alwood,  W.  B. 

1892  Brown  spot.     In  Four  diseases  of  the  apple,  and  treatment  of 

same.     Virginia  Agr.  and  Mech.  Coll.  Agr.  Exp.  Sta.     Bui. 
17:  59, '62. 

Describes  a  leaf  disease  and  uses  the  name  hrown  spot.      Notes  three  successive  out- 
breaks in  a  summer.     Questions  whether  Phyllosticla  pirina  is  the  cause. 

1893  Injurious  insects  and  diseases  of  plants  with  remedial  measures 

for  the  same.     Virginia  Agr.  and  Mech.  Coll.  Agr.  Exp.  Sta. 
Bui.  24:1-40.     Illustrated. 

The  apple  orchards  of  Virginia  said   (p.   24)  to  suffer  chiefly  from  two  foliage  diseases 
•    one  of  which  is  called  brown  spot,  attributed  to  the  attacks  of  Phylloslicta  pirina. 

1898  a  The  leaf-spot  disease  of  apple,  Phyllosticta  pirina  Sacc,  and 
several  unrelated  forms  occurring  therewith.  Amer.  Assoc. 
Adv.  Sci.     Proc.  47:413. 

Records   the  following  fungi  occurring  with    Phyllosticta  pirina  Sacc  :  Sphaeropsis 
Malorum  Peck,  Hendersonia  Mali,  and  an  undetermined  species. 


8  Translated  by  C.  D.  Sherbakoff,  formerly  of  the  Department  of  Plant  Pathology  at  Cornell  University. 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits     127 

1898  b  On  the  occurrence  of  a  yeast  form  in  the  life  cycle  of  the  black 
rot  of  apple,  Sphaeropsis  Maloram  Peck.  Amer.  Assoc.  Adv. 
Sci.     Proc.  47:  422. 

Records  the  discovery  of  a  yeast  form  occurring  in  cultures  of  this  fungus,  which 
on  isolation  and  reinfection  on  the  fruit  of  apple  produced  the  common  fruiting 
bodies  of  Sphaeropsis  Malorum. 

1902  Orchard  studies. — XV.  The  bitter  rot  of  apples.  Virginia  Agr. 
Exp.  Sta.     Bui.  142:250-274,  pi.  1-4. 

States  (p.  257)  that  Sphaeropsis  Malorum  Berk,  invades  fruit  already  decaying  from  the 
attacks  of  the  bitter  rot  fungus. 

Alwood,  W.  B.,  and  Price,  H.  L. 

1902  Orchard  stud^"es.— V.  Report  on  crab  apples.  Virginia  Agr. 
Exp.  Sta.     Bui.  132:3-14,  fig.  1-4. 

Note  (p.  6)  that  certain  varieties  are  especially  subject  to  the  black  rot  canker  (caused 
by  Sphaeropsis  Malorum). 

Amaud,  G. 

1912  Notes  phytopathologiques.  I.  Sphaeropsis  pseudodiplodia.  Mont- 
pellier  (France)  Ecole  Nat.  d'Agr.     Ann.  12:5-17,  fig.   1-5. 

Discusses  the  fungus  as  it  occurs  on  several  different  plants.  Notes  the  variable 
morphology  of  the  organism  and  reports  the  discovery  of  an  ascomycete  associated 
with  the  pycnidial  form.  The  ascomycete  is  named  Physalospora  Cydoniae  and  is  re- 
garded as  probably  the  perfect  stage  of  Sphaeropsis  pseudodiplodia. 

Arthur,  J.  C. 

1885  Quince  rot.  In  Report  of  the  Botanist.  New  York  (Geneva) 
Agr.  Exp.  Sta.     Ann.  rept.  3:372. 

Describes  symptoms,  and  proves  the  pathogenicity  of  the  fungus  (which  he  calls  Sphae- 
ropsis Cydoniae  C.  &  E.)  on  quince  fruit. 

Baccarini,  P. 

1890     Note  patologiche.     Ital.  nuovo  giom.  bot.  22:64-70. 

Reports  .Sphaeropsis  Malorum  on  pears,  apples,  and  peaches  in  storage.  Discusses 
sclerotia  and  pycnidial  development. 

Bailey,  L.  H. 

1907  The  healing  of  wounds.  In  The  pruning-book,  p.  76-132,  fig. 
68-110. 

Gives  a  chapter  on  the  healing  of  wounds,  taking  up  the  nature  of  wounds,  suggestions 
for  the  pruner,  dressings  for  wounds,  making  cuts. 

Baldwin,  C.  H. 

1912  Black  rot.  In  Some  important  diseases  of  apple.  Indiana  State 
Entomologist.     Rept.  5:249-252.     Illustrated. 

Gives  notes  on  black  rot,  leaf  spot,  and  canker. 

191 4  Black  rot  (New  York  apple-tree  canker  and  apple  leaf  spot). 
In  Apple  diseases.  Indiana  State  Entomologist.  Rept.  7: 
150-152.     Illustrated . 

Describes  the  nattue  of  the  injury. 

Bary,  A.  de 

1887  Comparative  morphology  and  biolog}^  of  the  fungi,  Mycetozoa, 
and  bacteria,  p.  1-525.  (Translated  by  H.  E.  F.'Oamsey 
and  I.  B.  Balfour.) 

Discusses  (p.  247)  types  of  pycnidial  formation  in  general. 


128  Bulletin  379 

Beach,  S.  A. 

1912  Black  rot.  In  Spraying  practice  for  orchard  and  garden.  Iowa 
Agr.  Exp.  Sta.     Bui.  127:  50-51.     Illustrated. 

Black  rot  observed  to  occur  on  some  of  the  summer  and  early  fall  varieties. 

Beach,  S.  A.,  Lowe,  V.  H.,  and  Stewart,  F.  C. 

1899  Apple  tree'  canker.  Also,  Leaf  spot.  In  Common  diseases  and 
insects  injurious  to  fruits.  New  York  (Geneva)  Agr.  Exp. 
Sta.     Bui.  170:382-384. 

Describe  canker,  caused  by  St>haeropsis  Malorum  Peck,  and  leaf  spot,  due  to  Phyllosticla 
spp.,  with  recommendations  for  control. 

Beal,  W.  J. 

1898  Diseases  of  the  apple.  Michigan  State  Hort.  Soc.  Ann.  rept. 
27:174-183,  pi.  1-4. 

Discusses  (p.  178)  symptoms  of  black  rot  of  apples,  and  compares  it  with  soft  rot  (caused 
by  Penicillium  expansum  Link). 

Berkeley,  M.  J. 

1836     Sphaeria  Malomm.     In  Hooker's  EngHsh  f^ora,  p.  257-258. 

Describes  the  fungus  Sphaeria  Malorum  Berk. 

i860  Sphaeropsis  Malorum  B.  In  Outlines  of  British  fungology,  p. 
316. 

Changes  the  generic  name  of  the  fungus  from  Sphaeria  to  Sphaeropsis. 

Berlese,  A.  N.,  and  Voglino,  P. 

1886  Macrophoma  Malorum  (Berk.)  Berl.  &  Vogl.  Cited  in  Sac- 
cardo's  Svll.  Fung.  10:197.  1892.  From  Veneto-Trentina 
Soc.     Atti".  1886:184. 

The  authors  divide  the  genus  Phoma  into  Macrophoma  and  Phoma,  the  basis  being  the 
length  of  the  pycnospores;  Phoma  Malorum  (Berk.)  Sacc.  becoming,  as  they  believe, 
Macrophoma  Malorum  (Berk.)  Berl.  &  Vogl. 

Bethune,  C.  J.  S. 

1909  Fimgus  diseases  and  insect  pests.  Also,  Cankers  on  apple  trees. 
Ontario  Agr.  Coll.  and  Exp.  Farm.     Ann.  rept.  34:26-32. 

Reports  (p.  29)  that  cankers  do  great  damage  along  the  north  shore  of  Lake  Ontario. 
Says  (p.  29)  that  spores  of  Sphaeropsis  Malorum  are  carried  by  the  wind. 

191  o  Black  rot  canker  (Sphaeropsis  Malorum).  Ontario  Agr.  Coll.  and 
Exp.  Farm.     Ann.  rept.  35:35-36. 

states  that  black  rot  canker  apparently  can  be  successfully  controlled  by  pruning  out 
dead  branches,  cutting  out  cankers,  and  coating  the  bark  with  spray. 

Bommcr,  E.,  and  Rousseau,  M. 

1885     Florule  mycologique  des  environs  de  BruxeUes,  p.  3-353. 

sphaeropsis  Malorum  Berk,  is  listed  (p.  257)  on  fallen  apples. 

Brooks,  Charles 

1907  Diseases  of  the  apple.  In  Seventeenth  and  eighteenth  annual 
reports.  New  Hampshire  Coll.  Agr.  Exp.  Sta.  Bui.  129: 
267-270,  pi.  15. 

Records  black  rot  and  cankers  due  to  Sphaeropsis  Malorum  Berk,  as  common;  records 
leaf  spot  due  to  Phyllosticla  pirina  Sacc.  and  P.  limitala  Peck  as  serious,  with  little 
or  no  effect  on  it  from  spraying.  States  that  majority  of  apple  limb  cankers  are 
caused  by  Sphaeropsis  Malorum  Berk.,  and  that  few  of  the  orchards  visited  did  not 
show  the  disease. 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits     129 

1909  Black  rot,  canker,  and  leaf  spot.  In  Some  apple  diseases.  New- 
Hampshire  Agr.  Exp.  Sta.     Bui.  144:123-126,  fig.  20-24. 

Discusses  occurrence,  symptoms,  etiology,  and  control  of  black  rot,  canker,  and  leaf 
spot.  Lists  the  folio wmg  fungi  as  associated  with  these  diseases:  Sphaeropsis 
Malorum,  Coniothyrium  pirina,  Coryneum  foliicolum,  Allernaria  sp.,  and  one  of  the 
Tuberculariae. 

1912  a  Black  rot,  canker,  and  leaf  spot.  In  Some  apple  diseases  and 
their  treatment.  New  Hampshire  Agr.  Exp.  Sta.  Bui. 
157:17-20,  fig.  20-24. 

Maintains  that  black  rot  does  considerable  damage  in  storage.     Outlines  sprayings 
which  are  said  to  be  fairly  efiEective  for  leaf  spot. 

1912  b  Fungicides  in  the  apple  orchard.  New  Hampshire  Agr.  Exp. 
Sta.     Bui.  161 : 1-15. 

Compares  different  fungicides  for  control  of  leaf  spot. 

Brooks,  Charles,  and  DeMeritt,  Margaret 

1912     Apple  leaf  spot.     Phytopath.  2:181-190,  pi.  17,  fig.  1-6. 

Give  an  account  of  the  etiology  of  leaf  spot,  paying  particular  attention  to  the  morpho- 
logical and  biological  variations  in  Sphaeropsis  Malorum.  Infection  shown  to  occur 
from  the  time  the  leaves  unfold  until  the  last  of  August.  Cultivation,  spraying,  and 
the  removal  of  cankers  given  as  the  important  control  measures. 

Brooks,  Charles,  Fisher,  D.  F.,  and  Cooley,  J.  S. 

1914  Apple  rots.     Phytopath.  4:403.     (Abstract.) 

List  several  species  of  fungi,  including  Sphaeropsis  Malorum,  which  were  isolated  from 
market  and  storage  apples. 

Bryce,  P.  I. 

191 5  Apple  leaf -spot  or  black  rot  canker.     Quebec  Soc.  Prot.  Plants 

from  Ins.  and  Fung.  Dis.     Ann.  rept.  7:86-90.     Illustrated. 

Gives  an  account  of  symptoms,  varietal  susceptibility,  and  control  of  the  disease. 

Bubak,  Fr. 

1909  Ein  kleiner  Beitrag  zur  Pilzflora  von  Niederosterreich.  Ann. 
myc.  7:59-62. 

sphaeropsis  Mali  (West.)  Sacc.  listed  (p.  62)  as  collected  on  Pirus  Malus  in  "  Hohe 
Warte"  bei  Wien. 

Burrill,  T.  J. 

1907  Bitter  rot  of  apples:  botanical  investigations.  Illinois  Univ. 
Agr.  Exp.  Sta.     Bui.  118:553-608. 

states  that  Sphaeropsis  Malorum  is  sometimes  associated  with  the  bitter  rot  fungus  in 
cankers.     The  former  organism  said  to  follow  the  latter  under  Illinois  conditions. 

Burrill,  T.  J.,  and  Blair,  J.  C. 

1 90 1  Apple  fruit-rots.  Illinois  Univ.  Agr.  Exp.  Sta.  Circ.  37:  (12 
pages,  unnumbered).     Illustrated. 

Special  attention  given  to  symptoms  of  black  rot,  caused  by  Sphaeropsis  Malorum.  Sug- 
gestion that  another  species  causes  canker.     Discussion  on  second  and  third  pages. 

Butler,  O. 

19 1 2  Report  of  the  Department  of  Botany.  In  Twenty-third  and 
twenty-fourth  reports.  New  Hampshire  Agr.  Exp.  Sta.  Bui. 
163 : 16-17. 

Mentions  the  work  of  Brooks,  which  appeared  later  in  Phytopathology  2  :i8i-i90  and 
was  published  jointly  by  Brooks  and  DeMeritt. 


130  Bulletin  379 

Caesar,  L. 

1909  Black  rot  canker  of  apple  trees.  In  Lime-siilphur  wash.  Part 
II. —  Practical  and  popular  treatment.  Ontario  Agr.  Dept. 
Bui.  177:59-61,  fig.  16. 

States  that  on  leaves  and  fruit  the  disease  is  seldom  serious,  but  cankers  often  do  great 
damage  especially  in  Prince  Edward  County,  Ontario. 

1912  Black  rot  canker.     In  Our  most  troublesome  orchard  insects 

and  diseases.      Ontario   Fruit   Growers'    Assoc.      Ann.   rept. 
44:22,  fig.  15. 

Author  is  convinced  that  the  fungus  follows  winter  injury. 

Card,  F.  W. 

1897     Notes  on  pruning.     Nebraska  Agr.  Exp.  Sta.     Bui.  50:  i-io. 

Concludes  from  experiments  that  lead  paint  is  the  best  material  for  covering  wounds; 
graftmg  wax  said  to  be  the  next  best;  coal  tar  found  to  prevent  checking,  but  seemed 
to  hinder  the  healing  process;  pine  tar  and  shellac  reported  as  unsatisfactory. 

Chase,  W.  W. 

1913  Apple  leaf  spot.     In  Principal  insects  and  diseases  of  the  apple 

in  Georgia.     Georgia  State  Bd.  Ent.     Bui.  38:40-41,  pi.   6, 
fig.  2. 

Leaf  spot  caused  by  Sphaeropsis  Malorum  said  to  be  one  of  the  most  destructive  apple 
foliage  diseases  in  Georgia. 

Chester,  F.  D. 

1901  a     Canker  in  apple  and  pear.     In  Pear  blight  and  pear  canker. 
Delaware  Coll.  Agr.  Exp.  Sta.     Bui.  52:6-8,  fig.  4-7. 

states  that  twigs  and  branches  bearing  pycnidia  of  Sphaeropsis   Malorum    Peck 
are  sources  of  infection. 

1901  b     Canker  in  the  apple  and  pear.     In  Report  of  the  Mycologist. 

Delaware  Coll.  Agr.  Exp.  Sta.    Ann.  rept.  12: 43-46,  fig.  4-7. 

(Same  as  1901  a.) 

1902  Pear  canker  treatment.     Also,  Canker  in  apples.    In  Sundry 

notes   on   plant   diseases.     Delaware   Coll.     Agr.    Exp.    Sta. 
Bui.  57:8-11,  fig.  5-6. 

Describes  symptoms  and  control  of  canker  of  pear  and  apple  caused  by  Sphaeropsis 
Malorum. 

Clement,  F.  M. 

1913  Winter  injury  in  orchards.  Quebec  Soc.  Prot.  Plants  from  Ins. 
and  Fung.  Dis.     Ann.  rept.  5:24-26. 

Says  that  frost  wounds  are  made  doubly  serious  if  not  treated  to  prevent  the  admission 
of  the  spores  of  saprophytic  fungi,  especially  those  of  the  black  rot  fungus,  with  the 
consequent  development  of  apple  canker. 

Clinton,  G.  P. 

1902  Black  rot,  Sphaeropsis  Malorum  Berk.  In  Apple  rots  in  IlHnois. 
Illinois  Univ.  Agr.  Exp.  Sta.     Bui.  69: 192-193,  pi.  b,  fig.  2. 

sphaeropsis  Malorum  Berk,  regarded  as  one  of  the  chief  causes  of  rotting  of  apples  in 
market. 

1904  Black  rot,  Sphaeropsis  Malorum  Pk.  In  Report  of  the  Botanist. 
Connecticut  (New  Haven)  Agr.  Exp.  Sta.  Ann.  rept.  27:298, 
342,  352,  pi.  II,  a. 

Black  rot  regarded  as  one  of  the  commonest  and  most  universal  diseases  of  the  apple. 
Noted  also  on  pear  and  quince. 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits     131 

1907  Winter  injury  and  canker,  Sphaeropsis  Malorum  Pk.  In  Report 
of  the  Botanist  for  1906.  Connecticut  (New  Haven)  Agr. 
Exp.  Sta.     Ann.  rept.  30:310-311,  pi.  17,  a. 

a  peculiar  limb  disease  of  the  apple  is  doubtfully  attributed  to  winter  injury  and 
Sphaeropsis  Malorum. 

191 5  Notes  on  plant  diseases  of  Connecticut.  In  Report  of  the 
Botanist  for  1913.  Connecticut  (New  Haven)  Agr.  Exp.  Sta. 
Ann.  rept.  38  (i9i4):i-29.     Illustrated. 

Black  rot  noted  on  stored  apples  (p.  s). 

Clinton,  G.  P.,  and  Britton,  W.  E. 

1910  Black  rot,  Sphaeropsis  Malorum.  In  Tests  of  summer  sprays  on 
apples  and  peaches  in  19 10.  Connecticut  (New  Haven)  Agr. 
Exp.  Sta.     Ann  rept.  33-34^59°.  pl-  21,  b. 

Authors  report  occurrence  of  black  rot  (due  to  Sphaeropsis  Malorum)  on  summer  and 
stored  winter  varieties.  State  that  the  use  of  insecticides  in  keeping  out  codling 
moth  lessens  the  rot  starting  from  this  cause. 

Cook,  M.  T. 

1913  Report  of  the  Plant  Pathologist.     New  Jersey  Agr.  Exp.  Sta. 

Ann.  rept.  33 -509-52 7- 

Black  rot  of  apple  and  quince,  caused  by  Sphaeropsis  Malorum,  among  the  diseases 
listed  (p.  512)  as  most  important  and  most  common  in  the  nurseries. 

1914  a     Black  rot  of  the  apple  and  quince.     In  Some  diseases  of  nursery 

stock.     New  Jersey  Agr.  Exp.  Sta.     Circ.  35:13-14,  fig.  9. 

Twig  and  leaf-spot  forms  of  the  disease  very  common  in  nurseries.  It  is  advised  that 
diseased  trees  should  never  be  set. 

1914  b  Black  rot  (Sphaeropsis  Malorum  Pk.).  In  Most  common 
diseases  of  the  year.  New  Jersey  Agr.  Exp.  Sta.  Ann.  rept. 
34:799,  809. 

Black  rot  of  apples  most  severe  on  Red  Astrachan.  Star,  Lawver,  Smokehouse.  Black 
rot  of  quince  reported  as  being  very  abundant  and  very  severe. 

Cooke,  M.  C. 

1892  Sphaeropsis  pomorum  (Schwz.).  In  Sphaeriaceae  imperfectae 
cognitae.     Grevillea  20:86. 

Suggests  that  Sphaeropsis  pomorum  (Schwz.)  [==  Sphaeria  pomorum  Schwz.]  is  probably 
the  same  as  Sphaeropsis  Malorum  Peck,  of  which  Phoma  Malorum  Berk.,  erected  by 
Saccardo,  is  possibly  a  younger  conditiori. 

Cooper,  J.  R. 

1913     The  control  of  canker  in  the  orchard.     Nebraska  hort.  3:2:1-2. 

Black  rot  canker  is  ranked  third  in  importance  among  cankers  in  Nebraska.  The  dis- 
cussion of  control  measures  is  directed  at  the  Illinois  blister  canker. 

Corbett,  L.  C. 

1900  Brown  spot,  frog  eye.  In  Fruit  diseases  and  how  to  treat  them. 
West  Virginia  Agr.  Exp.  Sta.     Bui.  66:202-204,  fig.  2. 

Author  considers  frog-eye,  or  brown  spot  (said  to  be  due  to  Phylloslicla  pirina),  more 
injurious  than  either  blight  or  scab. 


132  Bulletin  379 

Crabill,  C.  H. 

1915     The  frog-eye  leaf  spot  of  apples.     Virginia  Agr.  Exp.  Sta.     Bui. 
209:3-16,  fig.  1-5. 

Author  states  that  frog-eye  leaf  spot  is  the  most  prevalent  of  apple  foliage  diseases  in 
Virginia.  The  annual  losses  from  the  disease  are  said  to  be  heavy  in  that  State,  but 
systematic  spraying  has  controlled  the  disease  in  a  satisfactory  and  effective  manner. 
Symptoms  are  described.  Etiological  studies  are  tabulated,  and  from  his  experiments 
the  author  concludes  that  frog-eye  spots  are  initiated  by  Sphaeropsis  Malorum.  All 
other  fungi  with  which  he  deals  are  classed  as  facultative  parasites,  following  5. 
Malorum,  or  as  pure  saprophytes. 

Cummings,  M.  B. 

1909  Apple  orchard  survey  of  Niagara  County.     Cornell  Univ.  Agr. 

Exp.  vSta.     Bui.  262:277-320,  fig.  26-40. 

Gives  notes  (p.  304,  table  12)  on  economic  importance  of  canker. 

Dandeno,  J.  B. 

1906     A  stimulus  to  the  production  of  cellulose  and  starch.     Michigan 
Acad.  Sci.     Rept.  8:40-44. 

Claims  that  the  fungus  Sphaeropsis  Malorum  stimulates  the  cells  of  ripe  apple  fruit  to 
form  starch  and  to  thicken  the  cellulose  walls.  Suggests  that  starch  is  btiilt  up  first 
and  then  dissolved  and  built  into  cellulose,  the  process  going  on  until  the  fruit  is 
mummified  and  dry,  whereupon  it  is  in  a  state  of  preservation. 

Delacroix,  G. 

1903  a     Sur  un  chancre  du  pommier  produit  par  le  Sphaeropsis  Malorum 
Peck.     Soc.  Myc.  France.     Bui.  19: 132-140.     Illustrated. 

Gives  an  account  of  the  disease  which,  it  is  believed,  appeared  in  France  at  least 
as  early  as  1901.  Discusses  the  morphology  of  the  parasite  and  the  relationship 
of  the  myceliuni  to  the  tissues  of  limbs,  mentions  inoculation  experiments,  and 
suggests  control  measures. 

1903  b     Sur  I'identite  reelle  Sphaeropsis  Malorum  Peck.     Soc.   Myc. 
France.     6111.19:350-352. 

Reports  the  examination  of  the  f:;llowing  type  material:  Sphaeropsis  Malorum  Peck, 
5.  Malorum  Berk.,  Diplodia  maura  Cooke  &  Ellis,  D.  pseudodiplodia  Fckl.,  and 
Bolryodi plodia  Mali  P.  Brunaud.  Concludes  that  S.  Malorum,  D.  maura,  and  B. 
Mali  are  all  different,  and  that  S.  Malorum  in  France,  .S.  Malorum  Peck,  and  D. 
pseudodiplodia  Fckl.  are  identical.  States  that  since  D.  pseudodiplodia  was 
described  hcinre  S.  Malorum,  the  latter  name  should  disappear,  and  the  new  com- 
bination S.  pseudodiplodia  (Fckl.)   G.  Del.  is  proposed. 

Dickens,  A.,  and  Headlee,  T.  J. 

191 1     Spraying    the    apple    orchard.     Kansas    Agr.    Exp.    Sta.     Bui. 
174:251-292,  fig.  1-19. 

Give  an  account  of  experimental  work  in  the  control  of  black  rot  by  spraying.  Bor- 
deaux mixture  and  lime-sulfur  were  used  on  several  varieties. 

Douglass,  B.  W. 

1910  Black   rot.     In    Plant    diseases.     Indiana    State   Entomologist. 

Rept.  2  (1908-1909) :  135. 

The  disease  is  briefly  described. 

Duggar,  B.  M. 

1909     Black  rot  and  canker  of  pomaceous  fruits.     In  Fungous  diseases 
of  plants,  p.  303,  350-354,  fig-  169-172. 

A  discussion  of  habitat  relations,  etiology,  and  control  of  the  fungus. 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits     133 

Edgerton,  C.  W. 

1908     Two  little-known  Myxosporiums.     Ann.  myc.  6:48-53,  fig.  1-2. 

Points  out  similarity  and  difference  between  the  cankers  caused  by  Sphaeropsis  Malorum 
and  a  new  species  of  Myxosporium,  called  M.  corticolum.  The  synonymy  of  S. 
Malorum  is  given. 

Ellis,  J.  B. 

1880  On  the  variability  of  Sphaeria  Quercuum  Schw.  Philadelphia 
Acad.  Nat.  Sci.     Proc.  1879:66-70. 

Author  would  include  several  enumerated  species  of  Sphaeria,  Botryosphaeria,  Dothidea, 
and  Melogramma  under  one  species,  and  the  name  Melogramma  fuliginosa  is  accepted. 
Ascigerous  forms  accompanied  by  stylospore  forms  of  the  Diplodia  or  Sphaeropsis- 
type. 

Ellis,  J.  B.,  and  Everhart,  B.  M. 

1892     The  North  American  Pyrenomycetes,  p.  1-793,  pi.  1-41. 

Eustace,  H.  J. 

1908  Investigations  on  some  fruit  diseases.  New  York  (Geneva)  Agr. 
Exp.  Sta.     Bui.  297:29-48,  pi.  1-7. 

Shows  by  experiment  that  the  fungus  {Sphaeropsis  Malorum)  is  not  destroyed  but  its 
growth  is  retarded  in  storage  at  temperatures  ranging  from  29°  to  32°  F.  Gives  results 
of  sulfur  fumigation  in  storage. 

Evans,  I.  B.  P. 

1910  The  New  York  apple  tree  canker  or  black  rot  fungus  in  South 
Africa.     Transvaal  agr.  joum.  7:62-64,  pi.  7. 

Calls  attention  of  South  African  growers  to  the  presence  of  "another  imported  fungus, 
and  one  which  it  will  not  be  well  to  neglect." 

Faurot,  F.  W. 

1903  Black  rot.  In  Report  of  fungous  diseases  occurring  on  cultivated 
fruits  during  the  season  of  1902.  Missouri  State  Fruit  Exp. 
Sta.     Bui.  6:6-7. 

The  name  blossom  rot  is  employed  for  calyx-end  infections  on  apples.  Symptoms  are 
described. 

1912  Black  rot.  In  Common  orchard  troubles,  spray  mixtures,  and 
spray  calendar.  Missouri  State  Fruit  Exp.  Sta.  Bui.  23: 
14-15,  fig.  8-9. 

States  that  black  lot,  also  called  blossom-end  rot,  occurs  largely  on  fruits  of  which  the 
skin  has  been  broken,  and  that  owing  to  the  habits  of  the  fungus  it  is  not  controlled 
by  spraying. 

Floyd,  Bayard  F. 

1905  Apple  canker.  Black  rot.  In  Some  common  fungous  diseases 
and  their  treatment.  Missouri  State  Hort.  Soc.  Ann.  rept. 
48:432. 

Notes  that  windfall  apples  are  very  susceptible. 

Freeman,  E.  M. 

1905  Black  rot  of  apple  (Sphaeropsis  Malorum  Peck) .  7w  Minnesota 
plant  diseases,  p.  363-364,  fig.  194. 

Gives  a  short  general  account  of  black  rot,  leaf  spot,  and  canker. 


134  Bulletin  379 

Fiickel,  L. 

1869     Symbolae  mycologicae,  p.  1-459,  pl-  1-6. 

Descriptions  of  Diplodia  pseudodiplodia  Fckl.  (p.  393)  and  Diplodia  Malorum  Fckl. 
(p.  395). 

Galloway,  B.  T. 

1892  Report  on  the  experiments  made  in  1891  in  the  treatment  of 
plant  diseases.  U.  S.  Agr.  Dept.,  Veg.  Path.  Div.  Bill.  3 :  i- 
76.     Illustrated. 

Gives  (p.  30)  an  account  of  petal  and  young  fruit  infection  induced  by  Sphaeropsis 
Malorum. 

Garman,  H. 

1895  Spraying  experiments  in  1895.  Kentucky  Agr.  Exp.  Sta.  Bui. 
59 : 1 1 1-129.     Illustrated. 

sphaeropsis  Malorum  said  (p.  127)  to  be  the  cause  of  most  of  the  fruit  rot  in  the  State. 

1908  Brown  rot  of  apples.  In  i.  Spraying  apple  trees.  2.  Apple 
orchard  pests  in  Kentucky.  Kentucky  Agr.  Exp.  Sta.  Bui. 
133:8,65-66. 

The  disease  on  apple  fruit  (due  to  Sphaeropsis  Malorum)  is  called  brown  rot,  and  spray- 
ing experiments  for  the  control  of  the  disease  are  reported. 

Giddings,  N.  J. 

1908  Apple  canker.  In  The  occurrence  of  plant  diseases  in  1907. 
Vermont  Agr.  Exp.  vSta.     Ann.  rept.  20:331. 

Apple  canker,  caused  by  Sphaeropsis  Malorum,  said  to  be  rather  prevalent  in  some 
orchards.  The  statement  is  made  that  the  disease  is  easily  controlled  by  pruning 
and  spraying,  and  is  thus  kept  down  in  most  well-tended  orchards. 

Green,  W.  J.,  Selby,  A.  D.,  and  Gossard,  H.  A. 

1915  Spraying  program  for  orchards  with  combinations  recommended. 
Ohio  Agr.  Exp.  Sta.     Circ.  149:53-60. 

Suggest  (p.  54-55)  a  combination  of  insecticide  and  fungicide  for  control  of  codling 
moth,  apple  scab,  and  black  rot. 

Griffon,  E.,  and  Maublanc,  A. 

19 10  Sur   des  especes  de  Sphaeropsis  et  de   Diplodia  parasites  du 

poirier  et  du  pommier.     Soc.  Myc,  France.     Bui.  26:307-316. 
Illustrated. 

Discuss  symptoms,  and  several  species  of  fungi  on  apple  and  pear.  The  conclusion 
is  reached  that  these  trees  may  be  attacked  by  Sphaeropsis  and  Diplodia,  which  act 
as  wound  parasites.  The  species  involved  are  regarded  as  distinct  and  are  brief  y 
described;  these  are  Sphaeropsis  Malorum  Peck,  Sphaeropsis  pseudodiplodia  (Fckl.) 
Del.,  and  an  undetermined  Diplodia. 

Giissow,  H.  T. 

191 1  Black   rot    (Sphaeropsis   Malorum   Peck.).     In   Report   of   the 

Dominion  Botanist.     Experimental  Farms  (Canada).     Rept. 
1911:  246-247. 

symptoms  and  control. 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits     135 

Halsted,  B,  D. 

1892  The  black  rot  of  the  quince.  In  Some  fungous  diseases  of  the 
quince  fruit.  New  Jersey  Agr.  Coll.  Exp.  Sta.  Bui.  91:8-10, 
fig-  5-6- 

Concludes  from  observation  and  experiment  that  the  species  of  Sphaeropsis  on  quince, 
apple,  and  pear  are  the  same.  States  that  the  fungus  causes  one  of  the  most  destruc- 
tive decays  of  the  quince,  and  that  the  spores  pass  through  the  air  or  are  carried  by 
insects. 

1894  Decays  of  mature  apples.  In  Report  of  the  Botanist.  New 
Jersey  Agr.  Exp.  Sta.     Ann.  rept.  14:367-377,  fig.  35-41- 

Symptoms  of  black  rot  well  described  (p.  374-375).  Author  makes  the  point  that  the 
fungus  probably  gains  access  through  remnants  of  the  flower  at  the  free  end. 

Harrison,  Charles 

1823  A  treatise  on  the  culture  and  management  of  fruit  trees,  p.  1-356. 
Illustrated. 

Attributes  (p.  341-343)  canker  to  such  causes  as  injudicious  pruning,  bruising,  nailing, 
bad  subsoil.     Surgical  methods  recommended. 

Hartig,  R. 

1894  Text-book  of  the  diseases  of  trees,  p.  1-33 1 .  (Translated  by  Somer- 
ville  and  Ward.) 

Hartley,  C.  P. 

1908  a     Some  apple  leaf-spot  fungi.     Science  n.  s.  27:  212. 

Reports  the  finding  of  eighteen  different  species  of  fungi  on  apple  leaf  spots  in  West 
Virginia,  Sphaeropsis  Malorum  being  among  the  common  ones. 

1908  b     Some  apple  leaf-spot  fungi.     Science  n.  s.  28:157-159. 

Gives  brief  historical  review  of  the  question-of  the  etiology  of  apple  leaf  spot.  A  list 
of  several  species  of  fungi  found  on  spotted  leaves  is  given,  and  inoculation  e.xperi- 
ments  with  certain  of  these  are  reported.  Results  indicate  that  Conioihyrium  pirina 
is  a  wound  parasite,  while  Coryneum  foliicolum  appeared  to  be  even  less  parasitic. 

1913     Twig  canker  on  black  birch.     Phytopath.  3:248-249. 

Reports  the  isolation  of  a  Sphaeropsis,  closely  resembling  5.  Malorum  but  with 
somewhat  smaller  spores,  from  swollen  cankered  black  birch  twigs  {Belula  lenta  L.). 
Inoculation  experiments  show  that  the  organism  is  parasitic  ofily  under  certain 
conditions,   nor  is  it  regarded  as  the  cause  of  the  swollen  cankers. 

Heald,  F.  D. 

1906  The  black-rot  o"  apples  due  to  Sclerotinia  fructigena.  Nebraska 
Agr.  Exp.  Sta.  Ann.  rept.  19:82-91.  Illustrated.  (See  also 
p.  22,  61.) 

Points  out  that  the  term  black  rot  is  a  confused  one,  having  been  used  for  diseases  caused 
by  both  Monilia  and  Sphaeropsis.  The  two  diseases  are  compared  and  contrasted 
as  to  symptoms. 

Hedges,  Florence,  and  Tenny,  L.  S. 

1912  A  knot  of  citrus  trees  caused  by  Sphaeropsis  tumefaciens.  U.  S. 
Plant  Indus.  Bur.     Bui.  247:1-74.     Illustrated. 

Hesler,  L.  R. 

1912  The  New  York  apple  tree  canker.  Indiana  Acad.  Sci.  Proc. 
1911:325-339,  fig.  1-7. 

Gives  data  concerning  the  geographical  distribution,  importance,  symptoms,  etiology, 
and  control  of  the  disease.     The  synonymy  of  the  fungus  is  reviewed. 


136  Bulletin  379 

1913  Physalospora  Cydoniae.     Phytopath.  3: 290-295.     Illustrated. 

Proves  expenmentally  the  genetic  connection  between  Physalospora  Cydoniae  and  Sphae- 
ropsis  Malorum. 

1914  Biological  strains  of  Sphaeropsis  Malorum.     Phytopath.  4:45. 

Results  of  cross-inoculation  work  with  the  fungus  from  several  host  plants  indicate  that 
there  is  one  large  morphological  species  embracing  many  biological  races. 

Hewitt,  J.  L.,  and  Hayhurst,  P. 

191 1  Diseases  of  apple  trees  and  fruit  caused  by  fungi  and  insects. 

Arkansas  Agr.  Exp.  Sta.     Bui.  109:409-445. 

Note  the  occurrence  of  black  rot  and  leaf  spot  in  Arkansas  (p.  438,  440-441). 

Howitt,  I.  E. 

1913     Fungus   diseases.     Ontario  Agr.    Coll.    and   Exp.    Farm.     Ann. 
rept.  38:29-30. 

Notes  the  occurrence  of  black  rot  canker  along  with  other  plant  diseases . 

Ingram,  Delia 

1912  Preliminary  notes  on  a  twig  blight  of  Quercus  prinus.     Phyto- 

path. 2: 96-97. 

Mentions  an  apparently  serious  disease  of  the  chestnut  oak  which  occurs  in  Connecticut, 
Virginia,  Maryland,  and  Pennsylvania.  The  organism  associated  with  the  disease  is 
said  to  agree  with  Dolhiorella  quercina  (C.  &  Ell.).     (Cf.  Rankin,  W.  H.,  1914.  P-  i4i-) 

Jehle,  R.  A. 

1913  The  brown  rot  canker  of  the  peach.     Phytopath.   3:105-110, 

pi.  10,  fig.  1-5. 

Reports  successful  use  of  coal  tar  on  wounds  of  peaches. 

Jones,  L.  R.,  and  Giddings,  N.  J. 

1907     Apple  canker.     In  The  occurrence  of  plant  diseases  in  Vermont 
in  1906.     Vermont  Agr.  Exp.  Sta.     Ann.  rept.  19:  231-232. 

The  fungus  Sphaeropsis  Malorum  said  to  continue  its  destructive  invasion  and  to  be  the 
cause  of  every  case  of  apple  canker  examined. 

Kern,  F.  D. 

1906  Indiana  plant  diseases  in  1905.     Purdue  Univ.   Agr.   Exp.  Sta. 

Bui.  111:121-134. 

Black  rot  of  the  apple,  pear,  and  quince  reported  (p.  125)  from  the  southern  part  of  the 
State  only. 

1907  Indiana  plant  diseases  in  1906.     Purdue  Univ.  Agr.  Exp.  Sta. 

Bui.  119:425-436. 

Mentions  (p.  428)  black  rot  and  canker  of  the  apple,  and  black  rot  of  quince,  present 
to  some  e.xtent  in  the  southern  part  of  the  State. 

Kinney,  L.  F. 

1895  a     Some  special  orchard  treatment  of  the  apple,  pear,  and  quince. 
Rhode  Island  Agr.  Exp.  Sta.     Bui.  31:1-17,  fig.  1-9. 

Reports  (p.  lo)  failure  to  control  black  rot  of  quince  by  spraying. 

1895  b     The  leaf  spot  of  the  apple  and  pear.     In  Horticultural  Division. 
Rhode  Island  Agr.  Exp.  Sta.     Ann.  rept.  7: 188-189,  fig.  7-8. 

Points  out  resemblance  of  injury  by  apple  leaf  miner  ( Tischeria  malifoliella  Clemens) 
to  apple  leaf  spot.  Spots  on  the  leaves,  and  spores  of  Phylloslicta  pirina,  which 
is  regarded  as  the  cause,  are  figured. 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits     137 

1895  c     The   brown    rot.     In    Horticultural    Division.     Rhode    Island 
Agr.  Exp.  Sta.     Ann.  rept.  7: 192-193,  fig.  12. 

Symptoms  are  given.       The  disease  on  the  fruit   (which  author    calk    brown  rot) 
and  spores  of  the  fungus  are  figured. 

Kirchner,  Oskar 

1906     Die   Krankheiten   und  Beschadigungen  unserer  landwirtschaft- 
lichen  i^ulturpflanzen,  p.  1-647. 

States  (p.  440)  that  the  canker  disease  of  apple  trees,  caused  by  Diplodia  pseudodi plodia 
Thiim.,  occurs  in  North  America,  France,  and  perhaps  Germany. 

Lamson,  H.  H. 

1897     Department   of  Bacteriology.     In  Ninth   annual  report.     New- 
Hampshire  Coll.  Agr.  Exp.  Sta.     Bui.  48:146-147. 

Bordeaux  mixture  said  to  have  had  little  efifect  in  controlling  leaf  spot  due  to  Phyllosticia 
pirina;  hence  work  was  directed  toward  its  control. 

1899     Apple  diseases.     In  Notes  on  apple  and  potato  diseases.     New 
Hampshire  Coll.  Agr.  Exp.  Sta.     Bui.  65:106-107,  fig.  38-39. 

Notes  the  serious  nature  of  leaf  spot,  which  is  said  to  be  caused  partly  at  least  by 
Phyllosticia  pirina. 

1901  Apple  tree  canker.     In  Thirteenth  annual  report.     New  Hamp- 

shire Coll.  Agr.  Exp.  Sta.     Bui.  87:130. 

Reports  the  presence  of  a  canker  which  is  believed  to  be  caused  by  a  fungus. 

1902  The  cold  storage  of  apples. —  Part  H.     Influence  of  cold  storage 

on  the  decay  of  apples.     Effect  of  wrapping  apples  in  paper. 
New  Hampshire  Coll.  Agr.  Exp.  Sta.     Bui.  93:75-81,  fig.  i. 

Sphaeropsis  Malorum  listed  (p.  75)  as  one  of  three  fungi  which  cause  most  of  the  rotting. 
Author  concludes  (p.  8i)  that  a  temperature  of  34°  F.  is  more  effective  than  40°  to 
43°  F.,  and  that  wrapping  the  fruit  is  of  decided  advantage  in  extending  the  keeping 
period  beyond  the  first  of  June.  Clean  newspaper  said  (p!  81)  to  be  just  as  effective 
as  more  expensive  paper. 

1903  Leaf  spot.     In  Fungous  diseases  and  spraying.     New  Hampshire 

Coll.  Agr.  Exp.  Sta.     Bui.  101:61-62.     Illustrated. 

Bordeaux  mixture  said  to  have  little  effect  in  controlling  leaf  spot  of  apple. 

Lewis,  C.  E. 

1909     Apple    diseases    caused   by  Coryneum    foliicolum    and    Phoma 
MaH.     Maine  Agr.  Exp.  Sta.       Bid.  170:183-200,  fig.  17-42. 

Reports  successful  infection  experiments  with  Sphaeropsis  Malorum  Peck  on  injured  bark 
and  on  uninjured  apple  leaves. 

19 1 2     Inoculation  experiments  with  fungi  associated  with  apple  leaf 
spot  and  canker.     Phytopath.  2:49-62. 

An  account  of  experiments  directed  toward  the  determination  of  the  parasitism  of 
such  fungi  as  Sphaeropsis  Malorum,  Phyllosticia  limitata'  Peck,  Coniothyrium  pirina 
(Sacc.)  Sheldon,  and  Coryneum  foliicolum  Fckl.  Author  concludes  that  a  part  of 
the  leaf  spot  in  Maine  is  due  to  Sphaeropsis  Malorum,  but  that  a  similar  spotting 
is  due  to  bordeaux  mixture;  that  Sphaeropsis  Malorum  is  the  only  fungus  isolated 
from  apple  leaves  in  the  State  which  causes  spots  when  inoculations  are  made  from 
pure  cultures;  and  that,  of  the  several  fungi  studied,  this  fungus  does  the  greatest 
damage  to  branches  and  to  twigs. 

Lewis,  1.  M. 

1908     Apple  leaf  spot.     New  Hampshire  Agr.  Exp.  Sta.     Ann.  rept. 
19-20:365-369,  pi.  8-9. 

Gives  a  historical  review  of  the  causal  nature  of  the  disease,  and  presents  inoculation 
and  control  data. 


138  Bulletin  379 

Lochhead,  William 

1905     Black  rot  canker.     Ontario  Agr.  Coll.  and  Exp.  Farm.     Ann. 
rept.  30:49,  fig.  4-5. 

Defines  the  term  canker  and  outlines  control  measures. 

1909     Apple  diseases.     In  Fungous  diseases  in  Quebec  in  1908.     Quebec 
Soc.  Prot.  Plants  from  Ins.  and  Fung.  Dis.     Ann.  rept.  1:31. 

The  prevalence  of  the  canker  form  of  this  disease  is  noted. 

Longyear,  B.  O. 

1904     Fungous  diseases  of  fruits  in  Michigan.     Michigan  State  Agr. 
Coll.  Exp.  Sta.     Spec.  bul.  25:1-68,  fig.  1-42. 

Records  the  black  rot  disease  of  apple  (p.  10-13).  pear  (p.  16),  and  quince  (p.  20). 

Lunge,  George 

1909  Coal  tar  and  ammonia,  Part  I,  chap,  i,  p.  1-15. 

Notes  differences  in  tars,  both  physical  and  chemical,  depending  on  the  origin.  Tar 
obtained  from  the  same  material  also  differs  very  much  in  composition,  according  to 
the  temperature  of  the  dry  distillation,  and  even  according  to  the  shape  of  the  retorts. 

Mc Alpine,  D. 

1902     Fungus  diseases  of  stone-fruit  trees  in  Australia  and  their  treat- 
ment, p.  1-165.     Illustrated. 

Lists  (p.  133,  134)   Diplodia  Maloriim  on  peach  and  plum  twigs. 

M'Cormack,  Edna  F. 

1910  Black   rot   of  the  apple.     In   Fungous   diseases   of  the  apple. 

Indiana  State  Entomologist.     Rept.  3:142-144.     Illustrated. 

Symptoms  discussed. 

McCready,  S.  B. 

1910  Black  rot  canker  (Sphaeropsis  Malorum  Peck).     Ontario  Agr. 

Coll.  and  Exp.  Farm.     Ann.  rept.  35:41-42. 

Brief  reference  to  hosts,  distribution,  etiology,  and  control. 

191 1  Black  rot  of  apple.     Ontario  Agr.  Coll.  and  Exp.  Farm.     Ann. 

rept.  36:37- 

Reports  use  of  lead  paint  and  gas  tar  as  wound  dressings;  the  latter  found  to  give 
better  protection. 

Mangin,  L. 

1901     Sur  une  nouvelle  maladie  des  pommiers  causee  par  le  "  Diplodia 
pseudo-diplodia."     Journ.  agr.  prat.  n.  s.  2:138-139. 

Reports  occurrence  of  the  disease  on  apple  branches  in  France,  and  gives  suggestions 
for  control. 

Morse,  V/.  J. 

1909     Notes   on   plant   diseases,    190S.     Maine  Agr.  Exp.  Sta.     Bul. 
164:1-28.     Illustrated. 

States  (p.  3-4)  that  Sphaeropsis  Malorum  from  leaf  spot  produced  decay  of  fruit  as  a 
result  of  artificial  inoculation.  States  (p.  lo)  that  self-boiled  lime-sulfur  seemed 
effective  in  controlling  leaf  spot. 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits     139 

Morse,  W.  J.,  and  Lewis,  C.  E. 

1910  Maine  apple  diseases.  Maine  Agr.  Exp.  Sta.  Bui.  185:335-392. 
Illustrated. 

Notes  on  the  etiology  of  leaf  spot  and  canker.  Canker  fungus  in  Maine  orchards  follows 
frost  injury. 

Munson,  W.  M. 

1909  Apple  enemies,  and  how  to  fight  them.  West  Virginia  Univ. 
Agr.  Exp.  Sta.     Bui.  121:353-366. 

Control  measures  for  leaf  spot  and  canker  given  (p.  360-362). 

Norton,  J.  B.  S.,  and  Symons,  T.  B. 

1907  Black-rot  (Sphaeropsis  Malorum).  In  Control  of  insect  pests  and 
diseases  of  Maryland  crops.  Maryland  Agr.  Exp.  Sta.  Bui. 
115:178. 

Give  brief  recommendations  for  the  control  of  black  rot,  leaf  spot,  and  canker. 

O'Gara,  P.  J. 

1902     Notes  on  canker  and  black-rot.     Science  n.  s.  16:434-435. 

Notes  a  case  of  girdling  of  branches  of  sumac  (Rhus  glabra  L.)  by  Sphaeropsis  rhoina 
(Schw.)  Starb.,  which  fungus,  after  careful  cultural  and  inoculation  experiments,  is 
regarded  as  probably  identical  with  Sphaeropsis  Malorum. 

Orton,  C.  R. 

1914  Black  rot.  Li  Some  orchard  diseases  and  their  treatment. 
Pennsylvania  State  Hort.  Assoc.     Proc.  55:  43-56.     Illustrated. 

Author  states  that  Sphaeropsis  Malorum  rarely  if  ever  produces  cankers  on  its  own 
initiative.  He  notes  its  wide  occurrence  on  various  plants,  and  says  that  a  perfect 
stage  has  recently  been  found  on  apple,  quince,  oak,  grape,  witch-hazel,  and  other 
hosts. 

Orton,  W.  A. 

1902-1907  Plant  diseases  in  the  United  States  in  1 901-1907.  U.  S. 
Agr.  Dept.  Yearbook  1901:669;  1902:715;  1903:550; 
1904:582-583;  1905:603-604;  1906:499-500;  1907:577- 
579- 

Gives  notes  or  the  occurrence    and   destructiveness  of   black  rot,  leaf   spot, 
and  canker  of  apple,  pear,  and  quince. 

Paddock,  Wendell 

1898  a    An  apple  canker.     Science  n.  s.  8:595-596. 

Reports  preliminary  experiments  in  canker  investigation.  Cultures  of  fungi  from 
cankers  showed  Schizophyllum  commune,  and  a  dark-spored  fungus  which  is  said 
to  resemble  Sphaeropsis  Malorum  Peck. 

1898  b     Additional  notes  on  an  apple  canker.     Science  n.  s.  8:  836-837. 

Suggests  that  Sphaeropsis  Malorum  Peck  is  parasitic  on  the  wood  of  pear  and  quince 
as  well  as  on  that  of  apple.  Cross-inoculations  of  the  fruits  of  these  three  plants 
gave  positive  results.  . 

1899  a    An  apple  canker.     Western  New  York  Hort.  Soc.     Proc.  44: 

58-63.     Illustrated. 

(See  1899  b,  of  which  this  is  a  popular  presentation.) 

1899  b     The    New    York    apple-tree    canker.     New    York    (Geneva) 
Agr.  Exp.  Sta.     Bid.  163:177-206,  pi.  1-6. 

Contains  an  account  of  host  relationships,  names  of  the  disease,  symptoms,  etiology, 
and  control.  Presents  conclusive  data  proving  that  Sphaeropsis  Malorum  is 
the  cause  of  canker  on  apple;  considerable  data  indicate  that  this  species  of 
Sphaeropsis  also  occurs  on  many  other  plants. 


I40  Bulletin  379 

1900  The  New  York  apple-tree  canker  (Second  report).  New  York 
(Geneva)  Agr.  Exp.  Sta.     Bill.  185:203-213,  pi.  1-4. 

States  that  Sphaeropsis  Malorum  occurs  on  apple,  pear,  and  quince  fruits,  and  on  apple, 
pear,  and  hawthorn  trees;  and  that  it  probably  occurs  on  several  other  plants,  but 
experiments  are  not  regarded  as  warranting  this  as  a  definite  conclusion.  Notes  that 
apple  leaves  are  occasionally  attacked  by  a  Sphaeropsis. 

Parkinson,  John 

1629     Paradisi  in  sole  paradisus  terrestris,  p.  1-612.     Illustrated. 

Briefly  outlines  (p.  55o)  the  nature  and  control  of  canker.     Of  historical  importance. 

Parrot,  P.  J.,  and  Fulton,  B.  B. 

1913  Notes  on  tree  crickets.     Journ.  econ.  ent.  6: 177-180.     Illustrated. 

Note  that  the  penetration  of  apple  bark  tissues  by  the  ovipositor  of  the  tree  cricket 
is  apparently  attended  by  an  infection  of  some  unknown  fungus  or  bacterium,  which 
results  in  the  formation  of  a  canker  indistinguishable  in  its  appearance  ?,nd  effects 
from  the  New  York  apple  tree  canker  or  the  fire  blight  canker. 

1914  Tree  crickets  injurious  to  orchard  and  garden  fruits.     New  York 

(Geneva)  Agr.  Exp.  Sta.     Bui.  388:415-461.     Illustrated. 

Authors  note  (p.  442)  that  injuries  by  tree  crickets  are  followed  by  some  infectious  agent, 
and  that  these  lesions,  in  their  external  appearances  and  their  effects,  resemble  super- 
ficially certain  stages  of  the  New  York  apple  tree  canker  caused  by  Sphaeropsis 
Malorum. 

Peck,  C.  H. 

1879  Report  of  the  Botanist.  New  York  State  Mus.  Nat.  Hist. 
Ann.  rept.  31:  19-60. 

Reports  (p.  20-21)  the  discovery  of  Sphaeropsis  Malorum  on  apple  fruits  in  Schoharie 
County. 

1881  Report  of  the  Botanist.  New  York  State  Mus.  Nat.  Hist. 
Ann.  rept.  34:24-58,  pi.  1-4. 

Describes  (p.  36)  symptoms  of  black  rot,  and  points  out  the  fact  that  the  distinction 
between  Sphaeropsis  and  Diplodia  sometimes  fails,  since  both  one-  and  two-celled 
spores  are  found  in  the  same  spore  case. 

Pollock,  J.  B.,  and  Kauffman,  C.  H. 

1905     Michigan  fungi.     Michigan  Acad.  Sci.     Rept.  7:  57-67. 

List  Sphaeropsis  Mali  (West.)  Sacc.  and  5.  Malorum  Peck. 

Potebma,  A. 

1907     Mycologische  Studien.     Ann.  myc.  5: 1-28,  pi.  1-3,  fig.  1-43. 

Discusses  mycelial  development,  including  spore  germination  and  protoplasmic 
streaming. 

1910  Beitrage  zur  Micromycetenfiora  Mittel-Ruszlands.  Ann.  myc. 
8:42-93,  fig.  1-38. 

States  that  the  pycnidia  of  S.  pseudodiplodia  (Fckl.)  Del.  arise  meristogenetically. 

1912  Pilzliche  Symbionten.  2.  Sphaeropsis  und  Helicomyces,  p.  28. 
Illustrated.     (Separate  sent  by  Potebnia  to  the  writer.) 

Price,  H.  L. 

1909  Black  rot.  In  Fighting  the  insect  pests  and  diseases  of  orchard, 
field,  and  garden  crops.  Virginia  Agr.  Exp.  Sta.  Circ. 
7:  lo-ii,  fig.  2. 

Recommendations  for  the  control  of  black  rot,  leaf  spot,  and  canker. 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits     141 

Quaintance,  A.  L.,  and  Scott,  W.  M. 

1912  Apple  leaf-spot.  In  The  more  important  insect  and  fungous 
enemies  of  the  fruit  and  foliage  of  the  apple.  U.  S.  Agr. 
Dept.     Farmers'  bul.  492:35-36,  fig.  20. 

Discuss  the  importance,  symptoms,  etiology,  and  control  of  apple  leaf  spot  caused  by 
Sphaeropsis  Malorum. 

Rankin,  W.  H. 

1914     Sphaeropsis  canker  of  Quercus  prinus.     Phjrtopath.  4:  44-45. 

Reports  Sphaeropsis  Malorum  Berk,  as  causing  twig  and  limb  cankers  on  chestnut  oak 
(Quercus  prinus  L.),  the  ncconnt  being  based  on  observation  and  inoculation  experi- 
ments. Regards  the  disease  as  the  one  described  by  Miss  Delia  Ingram  in 
Phytopathology  2  :  96  (p.  136). 

Reddick,  Donald 

1912  Frost  injur3^  New  York  State  Fruit  Growers'  Assoc.  Proc. 
11:34-41,  fig.  1-2. 

sphaeropsis  Malorum  said  to  be  usually  found  following  frost  injury. 

Reed,  H.  S. 

1908  Fall  blossoming  of  the  apple  induced  by  the  black  rot.  Plant 
world  11:  256-257. 

Notes  a  case  in  which  Sphaeropsis  Malorum  inhibited  the  normal  activities  of  an  apple 
tree,  allowing  the  tissues  to  carry  on  the  growth  which  would  normally  have  been 
deferred  for  several  months,  and  resulting  in  the  unfolding  of  normal  blossoms  on 
October  S. 

Reed,  H.  S.,  and  Cooley,  J.  S. 

191 1  Black  rot  (Sphaeropsis  Malorum).     In  Plant  diseases  in  Virginia 

in  the  years  1909  and  1910.     Virginia  (Polytech.  Inst.)  Agr. 
Exp.  Sta.     Ann.  rept.  1909-1910:  102-103,  fig-  21. 

Record  black  rot,  leaf  spot,  and  canker.  Report  pycnospores  discharging  from  pycnidia 
on  leaves  at  Blacksburg  on  June  25,  1910. 

Reed,  H.  S.,  Cooley,  J.  S.,  and  Rogers,  J.  T. 

1912  Foliage  diseases  of  the  apple.     Virginia   (Polytech.   Inst.)  Agr. 

Exp.  Sta.     Bul.  3^95:1-24,  fig.  1-13. 

Give  points  concerning  the  varietal  susceptibility  of  apples;  the  distribution,  importance, 
and  symptoms  of  the  disease;  and  the  life  history  of  the  fungus. 

Reed,  H.  S.,  and  Crabill,  C.  H. 

1913  Black  rot  (Sphaeropsis  Malorum).     In  Plant  diseases  in  Virginia 

in  the  years  191 1  and  1912.     Virginia '(Polytech.  Inst.)  Agr. 
Exp.  Sta.     Ann.  rept.  1911-1912:36,  fig.  3. 

Note  that  Sphaeropsis  Malorum  occurs  on  twigs  previously  killed  by  the  fire  blight 
organism.     Figure  a  multilocular  sterile  (?)  pycnidium. 

Reed,  H.  S.,  and  Stahl,  H.  S. 

191 1  The  erepsins  of  Glomerella  rufomaculans  and  Sphaeropsis 
Malorum.     Joum.  biol.  chem.  10:109-112. 

Authors  find  evidence  of  erepsin  produced  in  pure  cultures. 

Roberts,  J.  W. 

1913  The  "  rough-bark "  disease  of  the  Yellow  Newtown  app'e. 
U.  S.  Plant  Indus.  Bur.     Bul.  280:1-15,  pi.  1-3. 

Reports  (p.  9,  15)  Phomopsis  Mali,  a  new  species,  associated  with  Sphaeropsis  Malorum 
on  leaf  spots. 


142  Bulletin  379 

1914  Experiments  with  apple  leaf-spot  fungi.  Joum.  agr.  research 
2:57-66,  pi.  7,  fig.  1-3. 

Reports  the  isolation  of  several  species,  including  Sphaeropsis  Malorum.  from  apple  le^f 
spots.  A  new  species,  Alternaria  Mali,  is  in  the  list  and  is  technically  described. 
From  experiments  conducted  it  is  concluded  that  this  species  may  be  classed  as  a 
rather  strong  facultative  parasite. 

Rose,  D.  H. 

1914  Ring  rot.  Also,  Black  rot  (Sphaeropsis  Malorum).  In  Biennial 
report.  Missouri  State  Fruit  Exp.  Sta.  Bui.  24  (Bienn.  rept. 
I9i3-i9i4):20,  23-24,  pi.  5,  fig.  1-2. 

Ring  rot,  or  blossom-end  rot,  of  the  apple  fruit  thought  to  be  due  to  frost  injury  at 
blossoming  time,  followed  by  Sphaeropsis  Malorum  Peck.  Author  gives  notes  on  the 
destructiveness  of  black  rot. 

Ruggles,  A.  G.,  and  Stakman,  E.  C. 

191 1  Black  rot     In  Orchard  and  garden  spraying.     Minnesota  Univ. 

Agr.  Exp.  Sta.     Bui.  121:15. 

Symptoms  of  black  rot  given. 

Saccardo,  P.  A. 

1884a     Phoma  Malorum  (Berk.)  Sacc.     Syll.  Fung.  3:152-153. 

A  technical  Latin  description  is  given.     Author  lists  Sphaeropsis  Malorum  Berk,  in 
synonymy. 

1884  b     vSphaeropsis  Malorum  Peck.     Syll.  Fung.  3:294. 

Describes  the  fungus  which  Peck   (1881)   reports  and  regards  as  new,  thus  giving 
rise  to  the  name  Sphaeropsis  Malorum  Peck. 

Salmon,  E.  S. 

1907  Apple  leaf-spots.     Gard.  chron.  ser.  3:42:305-306,  fig.  120-124. 

A  brief  discussion  of  varietal  susceptibility  and  etiology  of  leaf  spots  caused  by  a  species 
of  Phyllosticta  and  one  of  Sphaeropsis.  The  author  is  in  doubt  as  to  whether  the 
latter  species  is  5.  Malorum. 

Scott,  W.  M. 

1906  The  control  of  apple  bitter-rot.     U.  S.  Plant  Indus.  Bur.     Bui. 

93:1-36,  pi.  1-8. 

Gives  (p.  27-33)  results  of  experiments  for  the  control  of  leaf  spot  in  connection  with 
apple  scab,  sooty  blotch,  and  bitter  rot. 

1908  Apple    leaf -spot.    In    Self -boiled    Hme-sulphur    mixture    as    a 

promising  fungicide.     U.  S.  Plant  Indus.  Bur.     Circ.  1:12. 

states  that  it  appears  that  leaf  spot  may  be  prevented  by  this  fungicide,  but  no  data 
are  cited. 

191 2  Apple  leaf -spot,  or  frog-eye.     In  Spraying  to  control  the  important 

insects  and  fungous  diseases  affecting  the  fruit  and  foliage  of 
the  apple.  Thomsen  Chemical  Co.  (Baltimore,  Md.).  Circ. 
4:14-15,  pi.  2,  fig.  I. 

Scott,  W.  M.,  and  Quaintance,  A.  L. 

1907  Leaf-spot   diseases.     In   Spraying   for   apple   diseases   and   the 

codling  moth  in  the  Ozarks.  U.  S.  Agr.  Dept.  Farmers'  bul. 
283  :  18-20,  fig.  3. 

Authors  give  recommendations  for  the  control  of  leaf  spot,  which,  as  they  state,  may 
be  due  to  Sphaeropsis  Malorum. 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits 


143 


Scott,  W.  M.,  and  Rorer,  J.  B. 

1908  Apple  leaf-spot  caused  by  Sphaeropsis  Malorum.     U.  S.  Plant 

Indus.  Bur.     Bvd.  121:45-54,  pi.  3-4. 

Authors  discuss  the  common  names  of  the  leaf  spot,  its  history,  geographical  occur- 
rence, importance,  symptoms,  etiology,  and  control.  Proof  of  the  pathogenicity  of 
Sphaeropsis  Malorum  on  apple  leaves  is  given,  together  with  a  study  of  the  role  of 
associated  fungi  on  leaf  spots. 

1909  Apple  blotch,  a  serious  disease  of  Southern  orchards.     U.   S. 

Plant  Indus.  Bur.     Bui.  144:1-28,  pi.  1-6. 

Authors  suggest  (p.  1 1)  that  Sphaeropsis  Malorum  is  a  factor  in  the  killing  of  apple  buds 
Further  investigation  is  deemed  desirable. 

Scribner,  F.  L. 

1890     Black-rot  of  the  apple.     Fungus  diseases  of  the  grape  and  other 
plants  and  their  treatment,  p.  81-83,  fig.  1606. 

Descriptions  of  the  disease  and  of  the  fungus,  called  Macrophoma  Malorum,  are  given. 

Seaver,  F.  J. 

1908     Color  variation  in  some  of  the  fungi.     Bui.  Torrey  Bot.  Club 
35:307-314- 

Points  out  that  color  characters  are  misleading  and  misused  in  the  Hypocreales. 

Selby,  A.  D. 

1900     A  condensed  handbook  of  the  diseases  of  cultivated  plants  in 
Ohio.     Ohio  Agr.  Exp.  Sta.     Bui.  121:1-69,  fig-  i-S4- 

Notes  (p.  14)  the  disease  on  the  leaves  and  fruit  of  apple  and  quince. 

1910  Black-rot.     In  A  brief  handbook  of  the  diseases  of  cultivated 

plants    in    Ohio.      Ohio    Agr.    Exp.    Sta.      Bui.  214:368-369, 
436,  fig.  1-105. 

Notes  the  importance  of  the  disease  in  Ohio. 

1913     Disease  s.usceptibility  of  apple  varieties  in  Ohio.     Ohio  Agr.  Exp. 
Sta.     Circ.  133:53-56- 

Indicates  degree  of  susceptibility  of  apple  varieties  to  black  rot  and  canker. 

Shear,  C.  L. 

1910     Life  history  of  Melanops  Quercutim  (Schw.)  Rehm  forma  Vitis 
Sacc.     Science  n.  s.  31:  748. 

Pure  cultures  of  ascospores  of  Melanops  Quercuum  (Schw.)  Rehm  forma  Vitis  Sacc. 
[^=  Bolryosphaeria  Berengeriana  de  "Hot.  =  B.  fuliginosa  (M.  &  N.)  E.  &  E.|  said  to 
produce  a  pycnidial  form  which  agrees  with  Sphaeropsis  Malorum  Berk,  and  Diplodia 
pseudodiplodia  Fckl. 

1913  Some  observations  on  phytopathological  problems  in  Europe  and 

America.     Phytopath.  3:77-87. 

sphaeropsis  Malorum  reported  (p.  81-82)  as  doing  no  noticeable  injury  in  orchards 
from  Italy  to  England. 

1914  Life  history  of  Sphaeropsis  Malorum  Berk.     Phytopath.  4:  48-49. 

Concludes  from  cultural  studies  the  ascosporic  form  of  Sphaeropsis  Malorum  Berk. 
is  Melanops  Quercuum  f.   Vitis. 

Shear,  C.  L.,  and  Wood,  Anna  K. 

1913     Studies  of  fungous  parasites  belonging  to  the  genus  Glomerella. 
U.  S.  Plant  Indus.  Bur.     Bui.  252:1-110.     Illustrated. 

Discuss  host  relationships,  variability,  and  parasitism  of  Glomerella. 


144  Bulletin  379 

Sheldon,  J.  L. 

1905  A  report  on  plant  diseases  of  the  State.  West  Virginia  Univ. 
Agr.  Exp.  Sta.     Bui.  96:69-99.     Illustrated. 

Black  rot  (p.  74).  leaf  spot  (p.  74-75),  and  canker  (p.  74)  reported. 

1907  The  taxonomy  of  a  leaf-spot  fungus  of  the  apple  and  other 

fruit-trees.     Torreya  7: 142-143. 

The  name  of  the  leaf  spot,  or  frog-eye,  organism  is  changed  from  Phyllostida  pirina  Sacc. 
to  Cohiothyrium  pirina  (Sacc.)  Sheldon. 

1908  Another  leaf -spot  fungus  of  the  apple.     Torreya  8:  139-141. 

Illosporium  malifolioriun  n.  sp.  is  said  to  be  concerned  with  the  leaf  spot,  in  a  secondary- 
manner.     This  fungus  is  described. 

Smith,  R.  I.,  and  Stevens,  F.  L. 

1910     Leaf  spot.     Also,  Black  rot.     In  Insects  and  fungous  diseases  of 
apple  and  pear.     North  Carohna  Agr.  Exp.  Sta.     Bui.  206: 
■    94,  95,  102-103,  %•  23. 

Call  the  disease  Sphaeropsose.  and  state  that  perhaps  one,  but  probably  several,  species 
are  responsible  for  leaf  spot. 

Stene,  A.  E. 

1910  Some  suggestions  for  Rhode  Island  apple  growers.  Rhode 
Island  State  Agr.  Bd.     Ann.  rept.  25:93-181.     Illustrated. 

Leaf  spots  and  canker  said  to  be  general  in  the  State  (p.  152-153). 

Stevens,  F.  L.,  and  Hall,  J.  G. 

1907  Sphaeropsis  on  apple  twigs.  In  Some  apple  diseases.  North 
Carolina  Agr.  Exp.  Sta.     Bill.  196:52-53. 

1909  a     Notes  on  plant  diseases  occurring  in  North  Carolina.     North 

Carolina  Agr.  Exp.  Sta.     Ann.  rept.  31:66-82,  fig.  i-io. 

Black  rot  and  canker  reported  (p.  66).  Sphaeropsis  and  an  ascomycetous  fungus 
found;  name  of  latter  not  given.  Sphaeropsis  reported  (p.  75)  as  a  canker-pro- 
ducing fungus  on  pear. 

1909  b  Variation  of  fungi  due  to  environment.  Bot.  gaz.  48:1-30, 
fig-  i~37-  ^^^  '^^^o  North  Carolina  Agr.  Exp.  Sta.  Ann. 
rept.  32  (1908-1909): 47-71,  fig.  1-37. 

Authors  discuss  observations  on  the  influence  of  environment  on  the  characters  of 
certain  fungi. 

Stevens,  F.  L.,  and  Sherman,  F. 

1903  The  black  rot.  Also,  The  black  rot  of  the  quince.  In  Insect 
and  fungus  enemies  of  the  apple,  pear,  and  quince,  with  methods 
of  treatment.  North  Carolina  Agr.  Exp.  Sta.  Bui.  183:72, 
82,  fig.  1-22. 

Symptoms  and  control  measures  of  black  rot  and  canker  given. 

Stewart,  F.  C. 

1896  A  new  leaf-spot  disease  of  apples.  In  Report  of  the  Mycologist. 
New  York  (Geneva)  Agr.  Exp.  Sta.  Ann.  rept.  14  (1895): 
545-546. 

Records  Phyllosticta  limitata  n.  sp.  on  apple  leaves  on  Long  Island.     Technical  descrip- 
tion given. 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits     145 

1904  Apple  canker.  In  Fungi  and  fungous  diseases.  Western  New- 
York  Hort.  Soc.     Proc.  49:  53. 

states  that  spraying  for  apple  canker  caused  by  Sphaeropsis  Malorum  is  only  a  partial 
preventive;  a  matter  not  understood. 

1909  Apple  leaf  spot.    In'  Recent  investigations  on  plant  diseases. 

Western  New  York  Hort.  Soc.     Proc.  54:  78-79. 

Believes  that  the  leaf  spot  problem  in  New  York  is  not  completely  solved.  Points  out 
that  spraying  often  fails  to  control. 

1910  Notes  on  New  York  plant  diseases,  I.     New  York  (Geneva)  Agr. 

Exp.  Sta.     Bui.  328:303-404,  pi.  1-18. 

Discusses  (p.  312-313)  occurrence  of  leaf  spot  in  New  York.  Gives  (p.  323-324)  an 
account  of  a  peculiar  disease  of  the  trunk  of  Walbridge  apples  and  suggests  that 
Sphaeropsis  Malorum  may  have  been  a  factor  in  producing  the  same.  Suspects  (p.  377- 
379)  that  the  fungus  also  causes  the  failure  of  grafts  of  the  pear. 

Stewart,  F.  C,  and  Blodgett,  F.  H. 

1899  A  fruit-disease  survey  of  the  Hudson  Valley  in  1899.     New  York 

(Geneva)  Agr.  Exp.  Sta.     Bui.  167:273-308,  pi.  1-4. 

Notes  on  the  geographical  occurrence  of  the  leaf  spot  and  canker  in  the  Hudson  Valley 
(p.  283,  284,  301-302). 

Stewart,  F.  C,  and  Eustace,  H.  J. 

1902  Two  unusual  troubles  of  apple  foliage.     New  York   (Geneva) 

Agr.  Exp.  Sta.     Bui.  220:215-233,  pi.  1-5. 

Authors  conclude  that  spray  material  caused  spotting  of  apple  foliage;  suspect  the 
parasitism  of  Phyllosticta;  suggest  that  drops  of  rain  may  act  as  lenses  and  concen- 
trate the  sun's  rays,  overheating  the  tissue  beneath. 

Stewart,  F.  C,  Rolfs,  F.  M.,  and  Hall,  F.  H. 

1900  A  fruit-disease  survey  of  western  New  York  in  1900.     New  York 

(Geneva)  Agr.  Exp.  Sta.     Bui.  191:289-331,  pi.  1-6. 

Note  geographical  occurrence  of  the  disease  in  western  New  York. 

Stone,  G.  E. 

1914  Lime  and  sulfur  solutions.  Massachusetts  Agr.  Exp.  Sta. 
Circ.  39:1-4. 

Lime  and  sulfur  said  to  hold  leaf  spot  in  check,  and  believed  to  have  material  effect  on 
cankers. 

Stone,  G.  E.,  and  Fernald,  H.  T. 

1908  Canker.  In  Fungicides,  insecticides,  and  spraying  directions. 
Massachusetts  Agr.  Exp.  Sta.     Bui.  123:16. 

Suggestions  for  canker  control  are  given. 

Stone,  G.  E.,  and  Monahan,  N.  F. 

1907  The  lime  and  sulfur  mixture  as  a  fungicide.  In  Report  of  the 
Botanist.  Massachusetts  (Hatch)  Agr.  Exp.  Sta.  Ann.  rept. 
19: 167. 

State  that  observations  seem  to  indicate  that  spraying  with  lime  and  sulfur  succeeds  to 
some  extent  in  controlling  canker. 

Stone,  G.  E.,  and  Smith,  R.  E. 

1903  Apple-leaf  spot.     In  Report  of  the  Botanists.     Massachusetts 

(Hatch)  Agr.  Exp.  Sta.     Ann.  rept.  15:27,  32-34. 

Frost  followed  by  cold  wet  weather  caused  apple  leaf  spot. 


146  Bulletin  379 

Sturgis,  W,  C. 

1893  a  Black-rot  (Sphaeropsis  Malorum  Peck).  I«  Common  fungous 
diseases  and  their  treatment.  Connecticut  (New  Haven) 
Agr.  Exp.  Sta.     Bui.  115:6-7. 

Black  rot  of  apple,  quince,  and  pear  noted. 

1893  b  Black  rot  of  quinces.  In  Report  of  the  Mycologist.  Con- 
necticut (New  Haven)  Agr.  Exp.  Sta.     Ann.  rept.  1892 :  43-44. 

Description  of  black  rot  disease  of  quince  fruits. 

.  1894  Black  rot  (Sphaeropsis  Malorum  Peck).  In  Report  of  the 
Mycologist.  Connecticut  (New  Haven)  Agr.  Exp.  Sta. 
Ann.  rept.  17:  78-79. 

Reports  inoculation  and   spore   germination   data.     States   that   the   wind   and   other 
agencies  carry  the  fungus  spores. 

■*► 

Taft,  L.  R.,  and  Davis,  G.  C. 

1895  Black  rot  (Sphaeropsis  Malorum  Berk.).  In  The  pests  of  the 
orchard  and  garden.  Michigan  State  Agr.  Coll.  Exp.  Sta. 
Bui.  121:21. 

Briefly  describe  black  rot  and  give  suggestions  for  control. 

Taubenhaus,  J.  J. 

19 1 2  A  further  study  of  some  Gloeosporiums  and  their  relation  to  a 
sweet  pea  disease.     Phytopath.  2:  153-160,  pi.  16,  fig.  1-19. 

States  (p.  157)  in  a  footnote  that  black  rot  was  very  prevalent  in  the  very  dry  summer 

of  IQII. 

Taylor,  W.  A. 

1914  Fruit  diseases.  In  Report  of  the  Chief  of  the  Bureau  of  Plant 
Industry.     U.  S.  Agr.  Dept.     Rept.  1913:  105-133. 

States  (p.  107)  that  a  variety  of  Mdanops  Quercuum  has  been  shown  to  be  the  perfect 
stage  of  Sphaeropsis  Malorum. 

Thiimen,  F.  von 

1879     Fungi  pomicoH,  p.  108.     (Cited  from  Baccarini,  1890.) 

Waite,  M.  B. 

1898  a     An    apple    canker.     Western    New    York    Hort.    Soc.     Proc. 
43:9-11- 

Briefly  outlines  the  history  and  distribution  of  the  disease,  and  suggests  that  the 
cause  may  be  Schizophyllum  commune.     Control  measures  suggested. 

1898  b     An  apple  canker.     Rural  New-Yorker  57: 82,  fig.  32. 

Essentially  the  same  paper  as  the  preceding. 

1906  Fungicides  and  their  use  in  preventing  diseases  of  fruits.  U.  S. 
Agr.  Dept.     Farmers'  bul.  243:1-32,  fig.  1-17. 

Brief  notes  (p.  19)  on  control  of  black  rot,  leaf  spot,  and  canker. 

1908  Apple  leaf  bhght.  In  Diseases  of  orchard  trees  and  fruits. 
Pennsylvania  Agr.  Dept.     Ann.  rept.  13:450-452. 

Gives  treatment  for  leaf  spot. 

1910  Experiments  on  the  apple  with  some  new  and  little-known 
fungicides.     U.  S.  Plant  Indus.  Bur.     Circ.  58:1-19. 

Notes  on  leaf  spot. 


Black  Rot,  Leaf  Spot,  and  Canker  of  Pomaceous  Fruits     147 

Walker,  Leva  B. 

1908  A  new  form  of  Sphaeropsis  on  apples.  Nebraska  Agr.  Exp. 
Sta. .  Ann.  rept.  21:34-44,  fig.  i-io. 

Compares  typical  Sphaeropsis  Malorum  with  a  new  form,  the  latter  having  larger 
spores,  pycnidia  with  long  necks,  and  no  ostiole,  and  being  more  virulent  in  producing 
black  rot. 

Wallace,  Errett 

1913  Scab  disease  of  apples.  Cornell  Univ.  Agr.  Exp.  Sta.  Bui. 
335:541-624.     Illustrated. 

Warren,  G.  F.,  and  McCourt,  W.  E. 

1905  The  apple-tree  canker.     In  An  apple  orchard  survey  of  Wayne 

County,  ~  New   York.     Cornell    Univ.    Agr.    Exp.    Sta.     Bui. 
226:341-345,  fig.  86-87. 

Attention  is  given  to  the  economic  importance  of  the  canker  and  to  control  measures 
followed  by  the  growers  in  this  section  of  the  country.  It  is  said  that  very  few  mature 
Twenty  Ounce  trees  are  not  badly  cankered,  and  Esopus  suffers  seriously. 

Whetzel,  H.  H. 

1906  The  blight  canker  of  apple  and  pear  trees.     Western  New  York 

Hort.  Soc.     Proc.  51:36-45. 

..  Compares  fire-blight  and  New  York  apple-tree  cankers. 

1907  The  New  York  apple  tree  canker.     In  Fighting  the  fungi  in  their 

winter  quarters.     Cornell  reading-course  for  farmers,  March, 
1907,  p.  670-671,  fig.  365. 

Gives  symptoms  of  canker  and  measures  for  its  control. 

Whetzel,  H.  H.,  and  Stewart,  F.  C. 

1908  New  York  apple-tree  canker.     In  Insect  pests  and  plant  diseases. 

IV.  _The  control  of  plant  diseases      Cornell  Univ.  Agr.  Exp. 
Sta.     Bui.  252:35-),  fig.  165. 

Suggestions  for  canker  control  are  given. 

Wilcox,  E.  M. 

1905  Black  rot.  Also  Canker.  In  Diseases  of  the  apple,  cherry, 
peach,  pear,  and  plimi;  with  methods  of  treatment.  Alabama 
(Aubtirn)  Agr.  Exp.  Sta.     Bui.  132  :  89-93,  pl-  2,  fig.  6. 

Notes  on  symptoms  and  control  of  black  rot  and  canker. 

Wilcox,  E.  M.,  and  Stone,  R.  E. 

1909  Black  rot  (Sphaeropsis  Malorum).     In  Directions  for  the  control 

of  Nebraska  plant  diseases.     Nebraska  Agr.  Exp.  Sta.     Ann. 
rept.  22 :  3 1 . 

Give  schedule  for  control  of  canker  and  black  rot. 

Wilson,  G.  W. 

19 13  New  York  canker.  In  Notes  on  three  limb  diseases  of  apple. 
North  Carohna  Agr.  Exp.  Sta.     Ann.  rept.  35:47-49,  fig.  i. 

Brief  summary  of  history,  distribution,  importance,  and  symptoms  of  the  disease. 
Author  states  that  the  fungus  may  enter  the  bark  under  certain  conditions,  and  that  it 
does  not  travel  in  the  wood. 


148  Bulletin  379 

Wolf,  F.  A. 

19 10  The  prevalence  of  certain  parasitic  and  saprophytic  fungi  in 
orchards  as  determined  by  plate  cultures.  Plant  world 
13: 190-202. 

By  use  of  trap  cultures  the  author  concludes  that  at  no  time  during  the  period  in  which 
exposures  were  made  (September  to  May)  were  viable  spores  of  Sphaeropsis  Malorum 
present  in  the  atmosphere  of  the  orchard. 

1913     Control  of  apple  black-rot.     Phytopath.  3:288-289. 

Suggests  that  apple  mummies  are  a  source  of  the  inoculum.  Reports  that  in  the 
South  lime-sulfur  alone  is  effective  against  the  disease;  bordeaux  4-4-50  also 
satisfactory.     A  spraying  schedule  is  given. 


